Ah! You're thinking of A League of One!
Yeah. Diana beat him there, too. The problem? That story was non-canon. Not only that? Same problem as The Hiketeia: Batman was not prepared to fight Diana. She ambushed him. He had no chance. Almost any powered character can beat Batman when he isn't prepped for the fight.
I'm going to have to see a scan or something, because I've never seen Batman acknowledge Diana as being better than him at anything.
I've seen him acknowledge that Clark is a better person than he is. In MacDuffie's Injustice League story, he acknowledged Diana as "the best melee fighter in the world." Those are the only two occasions where I remember Batman acknowledging anyone as being better than him at anything.
Batman holds Superman in high regard. On paper, Superman should be able to stomp him whenever he so chose. Batman stomps Superman all the time.
Until and unless writers start to move away from this "Batgod" obsession, the basic rule is that Batman, with prep time, can crush anyone in the DCU. He just beat Darkseid in single combat and singlehandedly besieged Apokolips.
If the writers want Batman to beat Diana, they'll make it happen. One writer already had him drop Diana with one kick to the gut in one story. Another writer just had Batman stop her with an anti-Lasso that he just pulled out of nowhere. If the writers want Batman to negate all of Diana's powers and beat her like she owes him money? It's going to happen. And since Batman is their top earner? Lots of writers see the benefit of having stories where Batman can kick Wonder Woman's ass.
As am I!