Sam Shindler-Glass, 15, mastered a gruelling 6km course to win the Middlesex Schools under-17 title in Harrow.
Shindler-Glass said: "Four or five other races had already taken place that day so the course was churned up and muddy. I got into a pack of three at the front of the field, and with 200m to go put in a final spurt. Fortunately nobody was able to respond to it."
Shindler-Glass, who runs for of Ealing Southall and Middlesex AC, resumed his racing schedule four days later, finishing in 44th place at the National Cross Country Championships at Parliament Hill.
He said: "It was my best-ever run at Parliament Hill, so things are looking good for the Inter-Counties Championships this weekend and the English Schools race a week later."
Nathan Bloom, 13, placed 12th in the Middlesex Schools under-15 Championships, while Nathaniel Lane placed ninth in the Welsh National Championships.