That's a tough situation, but with only one other player you've got a good chance of him staying in the hand chasing draws. But of course you also have to look out for made
hands, obviously. The chance of flopping a straight with 1-gap connectors (e.g., QT) are 101.1 to 1. If the flop is also 2 or 3-card suited, you've also got a good chance of getting a lot of money in the pot while the other guy chases a flush. The
odds that he actually flopped the flush are 117.1 to 1.
However, it really depends on how lucky you feel, and what position you're in. I'd play it aggressively (i.e., make him pay to chase) till he gives me good reason to think that I'm beat. I'm also hoping to see low unsuited cards on the turn and river, with no T or Q.