She finished sixth in the final and only after did it dawn on the teenager how good she is and can be with more dedication and a better attitude.
"I have two years to improve so it's a good incentive to train hard," says Manning who will be among some of the country's elite female 800m runners lining up for the feature and final race of the annual Sylvia Potts Memorial Classic in Hastings today at 7.25pm.
Classic queen Angie Smit is returning to clinch a mind-boggling fourth consecutive title.
The 21-year-old Canterbury University student has clocked 2min 0.67sec in a European meeting but Hastings stalwart Allan Potts reckons she "hasn't done much this summer".
"She'll probably use this race in starting her build-up for the World Track and Field Championship in Moscow from August 10 to 18," Potts says.
If last year's race is anything to go by, it's difficult to see anyone eclipsing Smit although the likes of Kerry White, of Waikato (2:09.91), Arianna Harper, of Wellington (2:10.31) and Pippa Trevella, of Canterbury (2:11.42) will no doubt see the champion's clean pair of sprigs if they keep up.
Perhaps another exciting runner, Laura Nagel, of Napier, would have added a bit more zest but she has returned to Providence University, Rhode Island, in the United States after competing in Melbourne. The former Taradale High School pupil, who has competed in several Potts Classics as a teenager, ran 6min 08sec in a 2km race.
That, of course, begs the question why Manning, who has a personal best time of 2min 14.47sec, should even bother turning up at the Hawke's Bay Regional Sports Park this evening.
No, the Napier Athletics Club member doesn't have her head buried in the clouds of unrealistic expectations.
If anything, she and coach Sheila Smidt simply see it as a great opportunity to soak up the big-time atmosphere and to get a feel for what Manning needs to aspire to.
"If Holly can take 0.2 seconds off her personal best that'll be good enough," Smidt says, adding Manning intends to whittle the time to 2:12 at the North Island Championship in Masterton early April.
Manning, who will be a Year 12 student this year, started running in 4km cross-country events at Napier Central Primary School but the shorter middle-distance track beckoned in her first year at NGHS.
"Ms Smidt inspired me. She's amazing and I wouldn't be training as much if she wasn't there to push me along the track," Manning said.
Her genetic disposition in athletics is embedded in her parents. Her English mother ran 400m, 800m and 1500m races while her father from Hastings "did a bit of everything".
The couple met and married in Bromley, London, where Holly was born before the family settled in Napier when she was 2.
It's common to catch the Mannings, including Zac, 13, running in the harriers' 2-5km fun run in Napier on Tuesday nights.
"I love the feeling of the track and success after completing a race," says Holly Manning.
This time last year, Manning finished fifth or sixth in the B grade section of the Potts classic. She can't recall watching the classic "A" race but, needless to say, after 7.27pm today she won't forget a runner called Angie Smit.
Staying in the B grade today, she says, would have been a futile exercise because her PB of 2:24 last year, whittled to 2:20 in Tauranga last autumn, was a testimony to how far she had graduated.
"In the A grade, I'll just try to get a PB but, as Ms Smidt says, you can't always improve because if you could then it would be too easy," Manning said.
Her sixth place in the secondary school champs last month gives Manning an immense sense of satisfaction, considering most of the field were older than her.
A two-time Bay Under-15 hockey representative, she gave up the sport as the under-18s approached to focus on running.
"It was a bit too much at times," says the teenager who helps her busy father make waffle cones at their parlour, but it's mum who is saddled with chauffeuring duties to ensure she makes her myriad race meetings and training.
She isn't devoid of butterflies in her tummy before a big race, acknowledging a dose of jangled nerves has its advantages.
"But then everyone is in the same boat," she says with a smile.
Manning hopes to score an American scholarship to Stony Brook University in New York.
Finding consistency around the 2:14 mark while training will build a perfect preamble to another exciting chapter in the life of a girl who could one day assume the mantle of 800m supremacy.