Three-time Grand Slam champion and former world No 1 Andy Murray's professional tennis career could be over.

The 31-year-old Scottish star has been knocked out of the first Grand Slam of the year, going down to Spaniard Roberto Bautista Agut in a five set thriller in the first round of the Australian Open.

After losing the first two sets 6-4, 6-4, it looked like Murray's potential last moments on a tennis court could end in sad fashion, but with the crowd roaring him on, Murray fought back, winning consecutive tiebreaks to send the match to a deciding set.

However, a comeback victory was too much to ask for, as Murray couldn't produce any more magic in the fifth set, losing it 6-2 as Bautista Agut advanced to the second round.

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Murray, who has had a horror injury run over the past two years, announced late last week that the event at Melbourne Park may be his last tournament.

He said he'd hoped to be able to get to Wimbledon but his body may not allow him to last that long with another operation.

After barely surviving a practice session with Novak Djokovic on Thursday, Murray had to be excused early in his interview when he broke down in tears when asked about his fitness.

Murray didn't confirm any immediate plans after his defeat to Bautista Agut.

9.55pm: Disturbing scenes at Melbourne Park

On Margaret Court Arena, Aussie Ash Barty started strongly against the unseeded Luksika Kumkhum, taking the first set 6-2.

But there were distressing scenes on Court 5 when World No. 63 Andrea Petkovic retired from her clash with Romanian Irina-Camelia Begu.

Petkovic was leading 7-6 (7-3) 3-4 when he went down after hitting a forehand into the net.

She rolled over onto her back and was attended to by medical staff but was unable to continue playing.

9.40pm: Fans slam Aussie Open coverage

Aussie viewers have reacted angrily to Channel 9's $350 million Australian Open experiment.

Social media was littered on the opening day of the year's first grand slam with scathing criticism of Nine's first day of covering the two-week spectacle at Melbourne Park.

The network last year secured the Australian Open in a $300 million six-year deal as part of the greatest shake-up to Australian television's summer sport landscape.

Nine went on to secure the rights to the 2019 Australian Open in August in a deal worth an additional $48.5 million following revelations of scheduling conflicts between former broadcaster Channel 7's coverage of the 2019 event and its new cricket broadcast project with Fox Sports.

Nine spared no expense in assembling a high-profile commentary team to match its financial investment — headlined by the headhunting of American Jim Courier and Aussie fan-favourite Todd Woodbridge from Seven's stable.

Unfortunately, in the eyes of many, the coverage has fallen flat.

The Channel 9 team hasn't been so warmly received just yet. Photo / News Corp Australia
The Channel 9 team hasn't been so warmly received just yet. Photo / News Corp Australia

Aussie fans flocked to Twitter on Monday, punching holes in Nine's opening day broadcast from Melbourne Park.

The tennis identities assembled by Nine, including hosts Erin Molan and Tony Jones, were again a source of aggravation for many Aussie viewers, but the greatest cause for concern for many was the many unfamiliar voices behind the microphone after more than 40 years of Seven broadcasting the Aussie Open.

Nine's star-studded commentary stable was among the broadcast services used by the Australian Open's Host Broadcast Service — sent to more than 900 million potential viewers around the world.

However, the decision to use international commentators, including those from the HBS feed, during the opening day rubbed many fans raw.

Day one coverage prominently featured popular Aussie caller Peter Donegan's tag-team commentary with South African great Wayne Ferreira during World No. 2 Rafael Nadal's win over Aussie James Duckworth — the second match on Rod Laver Arena.

Nine followed that match with its pairing of Woodbridge and Courier for Alex de Minaur's first-round match against Pedro Souza.

The star-studded pairing of Jelena Dokic and John Fitzgerald covered Maria Sharapova's 6-0 6-0 win over Harriet Dart in the first televised match of the day.

Viewers on social media appeared to be unimpressed at the standard of commentary.

Many other fans took to social media to vent their annual frustrations about scheduling, tennis identities and general presentation.

Nine announced last year its stable of tennis commentary stars would include hosts James Bracey, Rebecca Maddern and Jones as well as commentators Woodbridge, Courier, Dokic, Alicia Molik, Dylan Alcott, Sam Smith, Fitzgerald, Donegan, Geoff Masters Roger Rasheed.

8.20pm: Handshake causes a stir

The aftermath to Barbora Strycova's match with Yulia Putintseva was as interesting as the on-court action itself.

Putintseva won 6-4 7-6 (7-1) but the pair's frosty relationship was evident when they came to the net to shake hands after the Kazakhstan star sealed her victory.

Putintseva defeated Strycova in the fourth round of last year's French Open and the pair have history when it comes to handshake fiascos. Strycova famously gave Elina Svitolina some weird skin-on-skin action in 2014 while Putintseva has some form in the matter too.

7.25pm: Aussie Demon makes his mark

Alex de Minaur is through to the second round after defeating Portugal's Pedro Sousa 6-4 7-5 6-4.

Fresh from claiming the Sydney International title, which required him to win his semi-final and final on the same day, the Australian 19-year-old overcame his opponent in a tick under three hours.

John Isner of the United States reacts during his first-round loss to Reilly Opelka. Photo / Getty
John Isner of the United States reacts during his first-round loss to Reilly Opelka. Photo / Getty

7.20pm: Sakkari's shock upset, Isner falls

Maria Sakkari gave her Greek fans plenty to cheer about when she shocked the 22nd seeded Jelena Ostapenko in three sets.

The unseeded 23-year-old Sakkari defeated the 2017 French Open champion 6-1 3-6 6-2 in one hour and 49 minutes.

Sakkari was supported by a hoard of vocal supporters, who made their way to Melbourne Arena after watching fellow Greek star Stefanos Tsitsipas book his place in the second round earlier in the day.

Another upset followed not long after their match as John Isner became the first top-10 player to lose, bowing out in the first round to fellow giant Reilly Opelka.

The battle between the big dogs was the tallest ever grand slam match as the 2.1m Opelka defeated 2.08m Isner in four sets that all went to tiebreaks, taking two hours and 58 minutes to complete a 7-6 (7-4) 7-6 (8-6) 6-7 (4-7) 7-6 (7-5) victory.

It was 21-year-old Opelka's first singles victory at a major. He sent down 40 aces to Isner's 47.

Rafael Nadal hits a backhand in his first-round match against James Duckworth of Australia. Photo / Getty
Rafael Nadal hits a backhand in his first-round match against James Duckworth of Australia. Photo / Getty

5.30pm: Nadal opens his account

Rafael Nadal held off a third-set fightback from Aussie James Duckworth to claim a 6-4 6-3 7-5 opening round win in Melbourne.

The Spaniard was in control for the whole match before looking shaky late in the third as Duckworth challenged the 32-year-old. But Nadal's class shone through in the end and he booked his spot in the second round.

"Not easy to come back after a lot of months especially against a player who is playing super aggressive," Nadal said. "It was difficult to be on rhythm.

"I'm very happy to be through, it's always difficult to start after injuries. It's so special to be back."

On Margaret Court Arena, No. 5 seed Sloane Stephens accounted for Taylor Townsend 6-4 6-2 — her first Australian Open win since 2014.

Men's 20th seed Grigor Dimitrov rebounded after dropping the first set against Janko Tipsarevic to win 4-6 6-3 6-1 6-4.

4.45pm: Aussies start strong

Two lesser-known Aussies made a bright start to their home grand slam, recording opening round wins.

Qualifier Astra Sharma, ranked 230 in the world, defeated compatriot Priscilla Hon 7-5 4-6 6-1.

Wildcard Zoe Hives, 22, also gave the home crowd reason to cheer when she defeated American Bethanie Mattek-Sands 6-1 6-2.

World No. 35 Danielle Collins scored the first major upset of the tournament, defeating No. 14 seed Julia Goerges in three sets.

South Africa's Kevin Anderson dropped the second set against Frenchman Adrian Mannarino but cruised through the last two to win 6-3 5-7 6-2 6-1 while women's No. 19 seed Caroline Garcia defeated French qualifier Jessika Ponchet 6-2 6-3.

The 11th seeded Aryna Sabalenka took just over an hour to advance to the second round, easing past World No. 167 Anna Kalinskaya in straight sets.

Britain's Katie Boulter reacts when thinking she won her match during the tie-break final set in her first-round match against Ekaterina Makarova of Russia. Photo / Getty
Britain's Katie Boulter reacts when thinking she won her match during the tie-break final set in her first-round match against Ekaterina Makarova of Russia. Photo / Getty

3.40pm: Boulter goes the early bolt

The Australian Open "blew it" when the first ever match-deciding third set tiebreak unfolded at Melbourne Park on Monday.

Still celebrating her recent milestone of signing for the same agency as David Beckham and football megastar Neymar, Britain's Katie Boulter made history by becoming the first winner of an Australian Open first-to-10 third set tiebreak.

Unfortunately, the moment will be remembered for Boulter's brain fart in celebrating as if she had won the match when she went up 7-4 in the tiebreak against former Aussie Open semi-finalist Ekaterina Makarova.

Boulter jumped to the net after clinching a 7-4 lead before realising she needed another three points to progress to the second round.

In an attempt to avoid marathon deciding sets, the opening grand slam of the year has undergone a rule change in 2019. If the deciding set is tied at 6-6, players square off in a first-to-10 tiebreak.

The emerging British star went on to progress 6-0 4-6 7-6 (10-6) — but the magic of the moment was lost in the blundering scenes created by the new third-set tiebreak scoring system