Raducanu was given a wild-card entry into the tournament but looked right at home playing on No. 1 Court, winning eight straight games to take a 3-0 lead in the second set. But she struggled to put away Cirstea, failing to convert three straight break points in the next game. She was then broken and missed another five break points at 4-3 in a marathon game that lasted nearly 15 minutes.
And she needed three match points in the final game before Cirstea netted a forehand.
Gauff had an easier time completing a 6-3, 6-3 win over Kaja Juvan on Centre Court. Gauff finished with 21 winners and broke her opponent five times.
She will next play former Wimbledon champion Angelique Kerber, who beat Aliaksandra Sasnovich 2-6, 6-0, 6-1.
Raducanu will face Ajla Tomljanovic, who was involved in a heated exchange with Jelena Ostapenko after their third-round match. Tomljanovic accused Ostapenko of faking an injury to get a medical timeout while trailing 4-0 in the third set. They traded insults at the net after the match.
"You're behavior is terrible," Ostapenko said. "You have zero respect."
"You're the one to talk," Tomljanovic responded.
Tomljanovic won 4-6, 6-4, 6-2.
French Open champion Barbora Krejcikova beat Anastasija Sevastova 7-6 (1), 3-6, 7-5.
In men's play, Roger Federer reached the fourth round for a record-extending 18th time by beating Cameron Norrie 6-4, 6-4, 5-7, 6-4 on Centre Court. The eight-time Wimbledon champion had a slight wobble in the third set when he missed two break points at 5-5 and was then broken at love by Norrie.
After trading breaks in the fourth set, Federer broke again for a 5-4 lead.
He will play No. 23-seeded Lorenzo Sonego of Italy on Monday.
Norrie was the last British man remaining in the tournament.
Also, fourth-seeded Alexander Zverev beat American Taylor Fritz 6-7 (3), 6-4, 6-3, 7-6 (4) and No. 7 Matteo Berrettini advanced past Aljaz Bedene 6-4, 6-4, 6-4.
Nick Kyrgios had to retire with an abdominal injury after the second set of his third-round match against No. 16 Felix Auger-Aliassime. Kyrgios told a trainer he couldn't serve properly and was worried about tearing a muscle.
"It's getting worse and worse," Kyrgios said. "I'm trying but I can't even ... I can't serve anymore. I can't do it."
Kyrgios won the first set 6-2 but lost the second 6-1 on No. 1 Court.
The Australian is also playing mixed doubles with Venus Williams.
The men's singles started on a more light-hearted note when Kyrgios stepped onto the court only to realize he left his grass-court shoes in the locker room.
His mishap forced the two players to stand around for a couple of minutes before they could start their warmup.
"The one day I thought I was being a professional," Kyrgios joked.
A Wimbledon employee reunited him with the right shoes.
- AP