Red Bull Team Principal joked he was "surprised" it took Max Verstappen so long to assume the lead of the Belgian Grand Prix.
The F1 championship leader started sixth on the grid after a five-place grid penalty for a gearbox change, making his way up to second by the end of the first stint.
But teammate Sergio Perez was powerless to defend on lap 17 as Verstappen scythed into the lead before opening up a 22.3-second winning margin.
The Dutchman has made grid penalties almost obsolete over the past season and a half, such has been his dominance over the field.
"I was surprised it took him so long to get to the front, to be honest with you," quipped Horner, speaking to media including RacingNews365.
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"All jokes aside, he drove an incredible race. His pace in the first stint, passing the cars as he did, he did a great job to get to P2.
"After the stop, his race really came alive on the Medium tyre where he showed incredible speed.
"Checo didn't defend too hard because of the speed difference between the two of them and then thereafter it was about managing the rest of the race.
"Phenomenal to go into the summer break unbeaten in both Grands Prix and Sprints.
"It is beyond everyone's wildest imagination to be sitting in this position now."