Double world champion Verstappen is now 53 points clear of the Mexican - still his closest title rival - after seven of 22 races and could skip the next two and still be top of the standings.
So dominant was the Dutchman at Barcelona's Circuit de Catalunya that he finished 24 seconds clear of Mercedes' second placed Lewis Hamilton (38), the sport's most successful driver of all time.
Verstappen was fastest in every practice session, in qualifying and also took the bonus point for fastest lap of the race.
Perez started 11th and finished fourth in what he described as a race of "damage limitation", but insisted his confidence remained high.
Horner said he should take away the positives.
"Being Max Verstappen's teammate, take nothing away," Horner said. "There is not a driver out there today, I believe, that would have beaten Max in that car today.
"So he (Perez) is up against a driver that is at the top of his form. And that's very tough.
"Mentally it's a really tough thing to deal with but I think now there is that separation in the points, that may actually take the pressure off him a little and the expectation he's putting on himself.
"He needs to let go of that now and just be free to drive," added Horner.
Perez has won twice this season and could have taken the championship lead in Miami last month after starting on pole with Verstappen ninth.
Instead, Verstappen won to extend his lead over the Mexican who could finish only second.
Verstappen has led every lap since then, winning in Monaco from pole after a sensational qualifying lap and putting on a display of dominance in Spain, the circuit where he took his first win in 2016.
A third title, with several races to spare, is looking increasingly like a formality.
Perez started last in Monaco after crashing in qualifying, made five pit stops and was lapped twice by his teammate on his way to 16th place.
