Vettel dominated practice, qualifying and ultimately Sunday's grand prix to stretch his advantage to 60 points over Ferrari's Fernando Alonso, cruising home by more than 30 seconds despite being slowed by a safety car period midway through the race.
"His pace advantage was so significant." Horner told reporters. "Of course you have the advantage of running in clear air but we saw from Friday, the car was very quick here and we only really unleashed him in the window after the safety car and told him we needed to build again.
"But none of us expected him to hit (a lead of) 30 seconds within 15 laps. I think that's a combination of him having confidence in a car we have made progress with."
Horner paid tribute to lead designer Adrian Newey and his ability to juggle the responsibility of working on next year's car, when a raft of technical changes are being introduced, and maintaining the dominance of this year's vehicle.
Adrian and his team are doing an incredible job of balancing between the current development and the 2014 challenges," Horner added.
"High downforce circuits had not been our strong point earlier in the year and I think its testimony to the technical team and the hours that have gone in to come to a maximum downforce track and be right on the pace."
Horner felt for the team's second driver Mark Webber, who was forced to park his car on the last lap after climbing up to fourth before losing power in the closing stages.
"It was a bittersweet victory today because on the one hand we had such a dominant result by Seb and on the other for Mark to have an engine failure within two miles of the finish line," Horner said.
"We could see it happening about 10 laps out, we were losing water pressure and it had effectively run out with about a lap and a half to go.
"Then you are in the lap of the gods and we opted to keep pushing for the finish line and he nearly made it. That was harsh for him to race for two hours and have that failure on the last lap."
The Briton insisted that despite big leads in both the driver and constructor championships the team would not show any signs of complacency and were also looking forward to the challenge of having a competitive car ready for next season.
"Next year is a bit of a game changer and I think the power unit is going to become a key performance differentiator," he added.
"Whoever between Ferrari, Mercedes and Renault gets it right or wrong on the power unit side could have a major effect on the pecking order and performance.
"Nobody knows at the moment... everybody thinks they are doing alright but it's going to take the first half of next year to know that."