On the start line at Hyde Park last week there was a combined look of determination and conviction etched on Sonia O'Sullivan's face. Six minutes later it had given way to a mixture of despair and resignation. By the 2km point in the Flora Light 5km Challenge, the woman from Cobh was off the pace and fading.
It was a familiar feeling for her. The last time she tried to keep up with Paula Radcliffe, on the rain-sodden Olympiastadion track in Munich 13 months ago, she managed to do so for 2,400m of the European Championships 10,000m final.
On that occasion, when Radcliffe blitzed to victory in 30min 1.09sec, the second-fastest time in history, O'Sullivan left the track in a state somewhere twixt bemusement and shock.
"I've run quicker than I've ever run in my life," she said. "I've broken my Irish record by six seconds. And I've been beaten by 47 seconds, three-quarters of a lap."
Last Sunday, in central London, the final gap was 33 seconds. Radcliffe won in 14min 51sec, a new world-best time. O'Sullivan finished third in 15:24.
This morning the pair meet again: the 33-year-old Irishwoman who for so long was the European trail-blazer for women's distance running and the 29-year-old Briton who has been too hot for the rest of the world to handle these past 18 months.
O'Sullivan lines up as the defending champion in the women's race of the Bupa Great North Run. Radcliffe, though, starts as the odds-on favourite to win the half-marathon from Newcastle to South Shields - and to win it convincingly.
Radcliffe has won 13 road races in succession, a run which stretches back to June 2001. This year alone she has set world-best times on the road for 5km, 10km and the marathon. So how does a world-class runner like O'Sullivan - world 5,000m champion in 1995, Olympic 10,000m silver medallist in 2000 and world cross-country long-course and short-course champion in 1998 - set about tackling a woman who has been running out of this world?
"Well, I suppose with everybody you have an idea of what they're going to run or what they're capable of running," O'Sullivan said, pondering the task. "But there's always a chance that they're not going to run to that. So you have to give yourself every chance to go out and keep up for as long as you can. Then, I suppose, it gets to a point where you can't go with the pace any more and you have to be realistic - you just have to run the best that you can yourself.
"So, first of all, you start off and you say, 'OK, I'm in this race, I'm going to try to win'. But you can't win if someone's that much better than you. You have to really think about how you're going to run the race yourself rather than how somebody else is going to run it.
"Coming here, I just have to go out there and run as best I can. The half-marathon is a long way. The pace just wears you after a time. It's about whoever keeps it going for longer.
"I experienced it myself last year: that feeling of maintaining a strong pace and losing people. It's a great feeling when you're fit and you're able to do that. I'm sure Paula feels like that right now."
It would indeed be a shock if Radcliffe were not to prove too strong for the opposition today - even though she faces a who's who of women's distance running: O'Sullivan; Berhane Adere, winner of the world 10,000m title in Paris last month; Derartu Tulu, the reigning Olympic 10,000m champion; and Susan Chepkemei, holder of the fastest time for the half-marathon distance, an unratified 65min 44sec. It would be a shock, too, if the Bedfordshire woman were to fail to strike Olympic gold in Athens next summer, whether she attempted to succeed at 10,000m or the marathon.
The burden on her slender shoulders is all the heavier following the British team's failure to win a gold medal without her at the World Championships. It's the kind of weight of national expectation to which O'Sullivan has become accustomed in Ireland since she broke the world indoor 5,000m record back in 1991.
"It can be hard when things are not going so well," she said, relating her own experience. "But when things are going good, then it's great. If you're fit and ready, you can use all that to your benefit. It's just hard if you know deep down that you're not going to run as well as everybody expects you to. To then have to explain that is quite difficult."
O'Sullivan had one such difficulty at the World Championships last month. A runner's-up spot in the Weltklasse 3,000m in Zurich suggested a possible medal challenge in the 5,000m final in the Stade de France. A cold dictated otherwise. She trailed in 15th and last.
It has not been the best of years for O'Sullivan, but she has fought back too many times in her rollercoaster career to be written off just yet. Only last year she returned, after the birth of her second child, to win two European Championship silver medals and to set a world best time for 10 miles and a European best for 5km. She also ran the fastest half-marathon of the year: 67min 19sec, in the Great North Run.