Julia Armstrong and Louis Jones were surprise winners of the senior races at the third Sussex Cross Country League match at Lancing Manor where 300 competed.
It meant the league has now produced three different winners for the men's and women's events this season.
Armstrong triumphed after the leading runners, Fiona Clark (Crawley) and Julie Mitchell (Haywards Heath), went off course when clear.
Clark, who won the first of this season's races at Goodwood, led by a few yards from Mitchell.
But they failed to follow the marking and got lost.
Armstrong also headed in the wrong direction but had the presence of mind to turn back as soon as she discovered her mistake and re-joined the course without losing her position.
The Brighton and Hove veteran, far from comfortable in the recent Sussex Veterans Championships at the Pestalozzi Village when fifth, cantered home for a comfortable victory over Ann Morgan (Haywards Heath), who had been runner up in the Veterans Championship.
A distraught Clark did not finish but Mitchell, who would probably have won, managed to rejoin the race and finished 13th.
Mitchell said: "It happens and I had a good run."
Clark wanted the race declared void as some of the other runners further down the field had made a similar mistake.
Officials said it was a course that had been used before without difficulty and that there were no problems in the races that were held before and after the women's event.
Jones (Crawley) won the men's event over five miles in his first cross country race of the season.
He went clear within the first mile and stretched his lead to win by more than 100 yards.
His appearances this season have been on the road and he finished fifth in the Brighton 10km road race last month as well as running well in the high class Portsmouth five-mile event this month when 29th.
He said: "I've been training with Pat Davoren and I'm really looking for a good 5,000m track time next season and a good half-marathon.
"Although I won some Sussex titles when I was much younger, my studies at Brighton University restricted my time.
"Now I have finished and working part-time I can now organise my training much better "I went rather better than I had expected so I'm very pleased how things turned out.
"I'm pretty confident about the county championships at Stanmer Park next month."
Nigel Gates (Brighton and Hove), the county veterans champion, came through strongly to take second place ahead of Joel Kidger (Crawley) who is recovering from illness.
Kidger had to fight off the attentions of Brighton and Hove under-20 runner Jack Vail.
Brighton and Hove were comfortable winners of the team race ahead of Crawley and Chichester.
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