The opening half was far from a great advert for rugby union, with the game littered with 13 penalties and basic errors. The hosts held a 6-5 half-time through two Ceri Sweeney penalties, with Paul Sackey scoring a try for the visitors.
Sweeney added two of his three penalty attempts in the opening 15 minutes of the second half before he converted a touchdown from Sireli Naqelevuki on the hour.
The final 10 minutes were dominated by Quins but the Chiefs defence stood firm in front of 9,333 at Sandy Park - venue for the final of the competition in mid-March.
Exeter, fourth in the Aviva Premiership, gav e debuts to four of their summer signings including - Welsh international fly-half Sweeney, who led the side.
Harlequins, just two points behind the Chiefs in the Premiership, rested a number of senior players to give some younger players and those returning from injury an opportunity.
The Devon side gave away a string of penalties in the opening five minutes followed by a break up the middle by full-back Charlie Walker, before the ball was worked wide for former England wing Sackey to touchdown in the corner.
The Chiefs hit back immediately with a 15-metre penalty from Sweeney and he added a second 10 minutes later when his side were driving into the Quins' 22 where the visitors were penalised for coming in at the side.
Exeter continued to pin Quins back deep in their own half and the home side won a penalty at a scrum five metres from the line. The Chiefs opted for another scrum which the visitors turned over to clear up field.
Quins attempted to run the ball out of their own half and Walker looked to be racing through, only to run into a huge hit from full back Luke Arscott in his first start of the season due to injury.
Sweeney looked to have scored in the corner in the closing minutes of the half, following good work from Jack Nowell, Romana Graham and Kai Horstmann, only to be pulled back for a forward to leave the Chiefs with a slender 6-5 lead at the break.
It was a sloppy opening to the second half but Sweeney stretched the Chiefs with his third penalty.
The home side continued to press and a chip through from Arscott was chased by flanker Don Armand but Walker was there to save the try.
Minutes later the visitors were penalised in front of the posts. Sweeney, who had missed one attempt from out wide, made no mistake to add three further points to give them a 12-5 lead.
Midway through the half the Chiefs crossed for their only try of the game as centre Naqelevuki side-stepped over the line and Sweeney adding the simple conversion.
Quins went in search of the three scores needed to win in the final 10 minutes.
When the Chiefs won a turnover ball Sweeney attempted to clear up field but his kick was charged down by lock George Merrick on his debut.
The Welsh international scampered back to beat the England Under-20 international to the ball, where Quins were penalised.
- Sports & Recreation
- Ceri Sweeney