Predictable checkmate

Tonight was taco night and I played someone in an online chess tournament, but after a few minutes of strategic game play I had a checkmate lined up, and my opponent must of saw it too because instead of moving his newly promoted queen, he played rook to a1 to protect his queen, so I played rook takes queen, and now one of my rooks was threatening his, while my other rook was waiting to deliver a checkmate but so could the other one since my knight had white's king trapped, so white was feeling the pressure and resigned with no logical move?