The Chiefs opened the scoring with an early Mieres penalty, but a break through the middle from winger Niki Goneva and some slick hands from Toby Flood saw Thompstone cross in the corner. Flood added the extras from a tricky angle.
In the second half it was Thompstone who again scored for the Tigers, following a blunder in possession from Exeter deep in their own half. Flood neatly clipped the ball up to Matt Smith, who combined well with Bowden to send the winger over.
Thompstone completed his hat-trick late on after a turnover in midfield. The Tigers shipped the ball wide before Smith grubbered the ball in behind the Chiefs' defence, Thompstone racing through to collect and score under the posts.
The Chiefs' points came from the boot of Mieres and a late pushover try as Leicester's set piece dominance told on the scoresheet.