INDIANAPOLIS – For the second straight match, James Blake found a way to survive and advance.

The American struggled early in the first set and fought off two set points in the second before defeating Jun Woong-sun of South Korea 6-3, 7-5 in the second round at the Indianapolis Tennis Championships on Thursday.

Blake, ranked eighth in the world, got off to a similarly slow start in a 7-6 (2), 6-2 win against Dudi Sela on Tuesday.

“I definitely don't feel like this was my best match, but it got me through,” he said. “That's the most important thing. Sometimes, these matches are more important to win than the ones where you're playing well. I feel like when I'm playing well, I should be winning a lot of my matches. When you can manage to win the ones where you're not playing your best, it gives you the opportunity to play well the next day.”

Blake, the top seed, advanced to play Yen-Hsun Lu of Taiwan in the quarterfinals on Friday. Lu defeated American Rajeev Ram 6-1, 7-6 (1) on Thursday.

In the nightcap, American Sam Querrey rallied to beat compatriot Vincent Spadea 4-6, 6-3, 6-4. Querrey, seeded fourth and ranked 45th in the world, advanced to play Bobby Reynolds on Friday. Reynolds, another American, beat Alejandro Falla of Colombia 6-1, 6-1 on Thursday.

Blake led Jun 4-3 in the first set on Thursday before closing it out. In the second set, Jun had set point when Blake got an ace, then won the next three points to tie the set at 5-all. He handled the final two games, and clinched the match with his 10th ace.

“He gave me a little scare in the second set,” Blake said. “I think it had a little more to do with me than him.”

Blake seized momentum after fighting off the set points.

“Once I pulled that off, I thought I had new life, and I had a chance to get up and close that set out. Once I got another chance, I didn't want to let it go.”

Though Blake had some success with aces, he got just 49 percent of his first serves in, compared to 64 percent for Jun. Blake also struggled with his serve accuracy against Sela on Tuesday.

“That's one of the things I've been working on the last four weeks or so,” he said. “You never really expect results to come immediately, so I just have to make sure I don't get frustrated.”

Blake said he was too cautious against a man he's never played.

“I definitely shouldn't have had as much trouble as I did today,” he said. “I was probably feeling him out a little too much and not necessarily playing my game and playing a little passive.”

In doubles play, Scott Lipsky and David Martin defeated Daniel Nestor and Frederic Niemeyer 6-1, 7-6(4), and Ashley Fisher and Tripp Phillips defeated Rohan Bopanna and Aisam-Ul-Haq Qureshi 6-2, 1-0 after Bopanna retired with a back injury.