Canadian GP: Red Bull never expected Daniel Ricciardo's win

The reigning champion outfit had been braced for a tough time at the Circuit Gilles Villeneuve with its power deficit to rival Mercedes exposed on the track's long straights.

But it was able to capitalise when Mercedes hit trouble, allowing Ricciardo to pounce on the hobbled Nico Rosberg near the end.

Horner said: "I didn't believe that we could win this race, but the way Daniel has driven, the way he has made his passing moves, he just grabbed his opportunity.

"He has driven faultlessly all season and I am delighted for him that he won his first grand prix.

"It is a wonderful feeling for any driver. It was nice to have Seb [Vettel] on the podium to enjoy it with him and it is a very special day in his life and career.

"I am sure it will probably take a day or two for it to sink in."

KEY MOMENTS FOR RICCIARDO WIN

Horner says the key to Ricciardo getting past team-mate Sebastian Vettel was better pace around his second pitstop, with his in-lap being almost nine tenths quicker than the German's.

But Horner says the decisive moment that turned a podium into the win was the brave move that Ricciardo pulled around the outside of then second-placed runner Sergio Perez under braking for Turn 1.

Speaking about that phase around the second stops, Horner said: "Seb reported that he was in trouble with the tyres and was pushing us to look at strategy.

"So we went for the undercut to get him into a bit of clear air, and pitted Dan a lap later. His in-lap was massively impressive and it was the in-lap that did the damage.

"The pitstops were within 0.2 seconds of each other and that [lap] was how Dan got the jump on Seb.

"But the really decisive moment for him was his move around the outside of Perez into Turn 2 - that is what won the race.

"You could see even with our DRS open and everything we had, against the Mercedes powered car with his DRS closed, we could not make the pass.

"So Dan was opportunistic and in the end we took a bit of luck with Rosberg's misfortune, but you have to be there [to take advantage]."