Twenty-four hours after placing second in round 23 at Wiscombe Park, Mourant was the only driver to clock under 41 seconds in his winning effort, when he crossed the finishing line in 40.97 .
Mourant, whose first victory of the season was at Hoton Park, followed up his recent pair of second-place finishes at Bouley Bay, by taking 19 points at the weekend to move to within seven points of third place in the championship.
Mourant, who was fifth overall a year ago, remains fourth after finishing second to championship leader Trevor Willis on Saturday.
Willis clocked 41.46 and Mourant 41.58.
On Sunday, Mourant dipped under 41 seconds to claim maximum points while Richard Spedding and Willis placed second and third, respectively, in times of 41.27 and 41.41 .
Wallace Menzies, who is third, failed to claim any points in Sunday’s 24th round.
Mourant has now had three National round successes, two this season and his first last year at Bouley Bay, when he became the first Islander since 1962 to record a victory.
The next two rounds are at Shelsley Walsh in Worcestershire on 11 and 12 August.