The American scored twice and Gareth Bale impressed once again as Spurs booked their path through to the fourth round of the FA Cup with a convincing win at White Hart Lane
Dempsey opened the scoring with a simple close range finish from a Gareth Bale flick-on.
Bale doubled the lead, lashing home a deflected Dempsey shot in the penalty area to leave Joe Murphy with little chance of making a save.
And the USA international made it 3-0 in a blistering opening 45 minutes with a looping header from the Welshman’s corner.
Andre Villas-Boas made a handful of changes as Bale was welcomed back after suspension, while Benoit Assou-Ekotto made his long-awaited return from injury and Scott Parker was handed a start.
But Spurs showed no signs of finding it hard to gel and took the lead after just 14 minutes, when Sigurdsson’s curling free kick was nodded on by Bale and poked in by Dempsey at the back post.
Tottenham continued to dominate and went close again through Kyle Naughton, who saw his shot saved by the outstretched palm of Joe Murphy, before Bale flashed a shot across goal after gliding beyond a handful of Coventry players.
The Welsh winger went close again shortly after, taking the ball on his right foot and shooting wide, and Dempsey saw a half-volley blocked en route to goal by Emmanuel Adebayor as the League One side struggled to get to grips with Premier League opposition.
Bale was on target just minutes later though, blasting a deflected Dempsey shot beyond Murphy after the visitors had given the ball away cheaply in their own half.
And Bale and Dempsey combined again for the third goal, as the American rose to meet the winger’s corner at the back post, looping a header over the Coventry defence to hand Spurs a well-deserved advantage going into half time.
Tottenham continued to press for more goals after the interval and went close twice in quick succession.
A low Sigurdsson cross skidded across the six-yard box as Adebayor failed to connect for what would have been an open goal, before Steven Caulker met a Tom Huddlestone free kick but thundered wide.
Caulker would make amends though, blocking a Carl Baker shot as Coventry enjoyed its best spell of the game.
From the resulting corner, Richard Wood tested Brad Friedel with a header, but the American got down low to palm the ball away.
Spurs started to labor and Villas-Boas made a double substitution, replacing Sigurdsson and Scott Parker with Tom Carroll and Mousa Dembele.
And the home side would hold on to keep a clean sheet and book a comfortable path through to the fourth round.