Dillier, of BMC Racing, finished first in three hours 32 minutes 47 seconds following the 174.8-kilometre stag between Devon, Alta., and Red Deer. Sergei Tvetcov of Jelly Belly Cycling Team was just behind in second followed by Sagan in third.
Sagan, of Cannondale Pro Cycling, has a 26-second lead over Rohan Dennis of Team Garmin-Sharp. Tobias Ludvigsson is third while the 2011 Tour de France champion Cadel Evans is 36 seconds behind in fourth.
Victoria's Ryder Hesjedal is the top Canadian so far, 46 seconds behind at ninth overall.
The race cycles through prairies, badlands and foothills before ending up in downtown Calgary on Friday for a total 900 kilometres of racing.
The Tour is the largest and most highly ranked bike race ever held in Canada. It involves six top-ranked teams from the European Pro Tour and eight teams from the Continental tour, as well as the Canadian national team.
Its 117 riders include 11 winners of single stages or one-day events, five current national champions, two world champions and two major European tour winners, including Hesjedal, winner of the 2012 Giro d'Italia.
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