The double world champion set the third fastest time in qualifying, 0.465 seconds away from Perez's ultimate pace, but will move up to the front row on the grid as Charles Leclerc will cop at least a 10-place grid penalty for taking on new control electronics.
Despite a solid qualifying result, the consensus is that Aston Martin is much stronger in race trim, and Alonso explained that general long-run pace and a light touch with tyres will yield more performance on Sunday.
Regardless, Alonso does not expect to battle Perez for victory on the Jeddah Corniche Circuit, admitting that the Red Bull squad is "in another league" compared to the rest of the field.
He believes instead that Aston Martin will have to focus on beating the cars behind it, and suggest that the trio of Ferrari, Mercedes, and Alpine could all offer threats to the British squad's podium hopes.
"I don't know [if we can beat Perez] - I think we are not in that position yet," Alonso said.
"On pure pace, I think Red Bull is in another league and I think we have to concentrate more on the teams behind. So Ferrari will be very strong, Mercedes are strong, also Alpine - they are fast here.
"I think our race is just behind us. We saw today Max probably was in his league today in qualifying and he could not complete the qualifying with a mechanical issue.
"Even if we focus on our mirrors and try to keep the people behind, if anything happens in front, we will try to take the opportunity.
"I don't want to sound pessimistic, but if we see the pace in free practice, and in Bahrain, we have to be honest with ourselves and know that Red Bull is a little bit ahead of everyone.
"That's not the target tomorrow, to fight for the win with Checo. But, as I said before, Formula 1 is not exact mathematics, you know, anything can happen and today, Verstappen was P15. These things happen sometimes."
Alonso expects Aston Martin's rivals to create a tight race on Sunday, with small gaps between them throughout their varying long runs in the practice sessions.
Although outlining that good preparation was necessary to beat them, and he felt that the AMR23's tyre management was already strong, Alonso added that luck would be as much of a factor.
"It'll be a very tight race, I expect, and I think that it will be defined by small details: one will be the start, one will be the tyre management," he said. "The other one will be the strategy and probably the final one will be luck.
"Because we saw even last year with Checo, you know, how luck and a safety car can play a big factor here.
"We have to nail all of these points - I think as a team we are ready to take care of everything that is in our hands.
"The car seems to perform well on the long runs, seems very easy on tyres. So yeah, let's try to maximise our strengths and hopefully be lucky."
