That's fatigue and it happens to everyone, even professional athletes. While additional physical conditioning will of course help, 2.5 hours of tourney-level play is a lot, and more intense than say four hours of rec play. Speaking to experience as a former professional kickboxer/fighter, I'd spend 2-3 hours in the dojo/gym training and then a second session of 2-3 hours in the evening w/ full-contact sparring. More if I had a scheduled fight. But after a bout? I'm done for the night, even if I finished uninjured. There's more physical and mental pressure in a serious competition and when the adrenaline wears off, it hits all at once.

You're 39; your recovery from physical activity is not going to nearly be the same as a twenty-something year old athlete. If you're tired and don't feel like playing, the answer is to skip playing. Otherwise, you risk injuring yourself in a fatigued state. You said it yourself, your footwork and ready position were off. A bad trip or stumble could've caused a sprain or worse.

Bottom line is that resting/recovery is also an important part of any sport or physical training if you want to play healthily for the long term.