Five months ago, in the blinding heat of Marrakesh, the Irish athlete produced a sprint finish to win the world cross-country title over eight kilometres, forcing Radcliffe to accept the runner-up position for the second successive year.
Conditions in the Nepstadion are expected to be only slightly less harsh than they were in Morocco as the two women contest the 10,000 metres title in what promises to be one of the most absorbing races of the 17th European Championships.
Both are new to the event - Radcliffe's only previous experience of the distance came at Lisbon in April, when she became the fastest ever 10,000m debutant, running 30min 48.58 to take eight seconds off Liz McColgan's British record.
For the unpredictable O'Sullivan, this will be her first attempt at the distance on the track following a late decision to double up with the 5,000 metres.
The additional presence of Portugal's Olympic 10,000m champion, Fernando Ribeiro, who beat Radcliffe on the line in Lisbon to head this season's rankings, means that the race is certain to be a tactical battle.
Among those with whom Radcliffe has discussed a strategy for tonight's race is Brendan Foster, who won the European 5,000 metres title in Rome 24 years ago in similarly muggy conditions. He achieved his target by putting in two very fast laps which effectively broke up the field, then hanging on. He believes Radcliffe must make a move to take the running out of the faster finishers in the race in the second half of the event.
She was not willing to be drawn on her approach yesterday, although she hinted that the race would not be allowed to come down to a sprint finish. "There's nobody who is going to go to the front and start jogging," she said. "But whatever happens, I will have to adapt. I can't go in with a rigid race plan and say `that's it'."
She will, however, go in knowing she has never been in better form in her life, having spent three months of this year preparing at altitude in Font Romeu, in the Pyrenees.
So comfortable is she in the surroundings she first encountered while training for the 1995 World Championships that she has just bought a flat at which she intends to spend six months a year. The property is at the top end of the village, which is just under 2,000 metres above sea level. "I'm the highest resident in Font Romeu," she said.
Radcliffe's regime has been unrelenting - running twice a day for seven- day blocks with just one rest day in between, covering up to 120 miles a week, a distance she believes is worth 150 miles a week at sea level.
Other women who can stand that kind of pace are few and far between. She normally runs with men, including her boyfriend Gary Lough, who reached the 1500m final at the last European Championships, and Richard Nerurkar, who was also at Font Romeu preparing for Sunday's marathon here.
"There is more than just the physiological advantage of altitude training there," she said. "The surroundings are a part of it, and all the back- up at the centre, including physiotherapy. I have trained the same way this year as I did last year. It's a pattern that works for me."
Britain's women's team captain raised a few eyebrows when she missed the AAA trials last month. But her position had been cleared with the selectors - and the fact that she had doubled up at 5,000 and 1500 at the European Cup, winning the first and coming second in the latter, strengthened her case.
Radcliffe, disciplined and organised in everything she does, approaches her running in the same way as she did her studies, which won her a first class degree in European Studies from Loughborough University.
Her attitude as a competitor has always been first class too - her habit of nodding her head while running only serving to emphasise her commitment.
Radcliffe - who plans to move up to try a half marathon later this year in the Great North Run - is now a proven world class track performer - fifth in the Olympic 5,000m, and fourth, in last year's World Championship 5,000. What she desperately wants, though, is another first-class honour - in a championship. Maybe tonight.Reuse content