Well, the longer the fight is, the better it is for Cap. He has superhuman endurance and recovery. AS long as he can stay standing, he can wear Batman down. Steve has a physical advantage. Bruce's training can't match the SSS optimized speed, strength and agility of Cap. Cap's mind is also very quick, if not as smart as Bruce, he's at least as mentally agile and adaptable. Surprise is a tool that Batman needs to take full advantage of.
That said, Batman can more easily change up his fighting style and do unexpected things, once he figures out Steve is reading his attacks, he'll shift style and try something different. It just seems it would be so hard for him to strike a knockout blow, and the longer the fight goes on, the more his advantage dwindles.
I really think it's a toss-up, provided they were both somehow forced to fight to a conclusion, whereas otherwise it would likely end as it did above.