What could be bad about rising as high as No. 7 in the world tennis rankings at 29 and advancing to a second-week U.S. Open match against five-time champion Roger Federer a year later? By 2011, Mardy Fish had become a real major-tournament threat, a contender in 2012.

Except, he said Monday, that was when "what happened to me was that expectations changed. All of a sudden, it wasn't quite good enough to make the fourth round of a Grand Slam, when my whole life before that, it was an incredible achievement."

In fact, Fish had advanced to the Australian Open quarterfinals in 2007, the U.S. quarters the next year and the Wimbledon quarters in 2011. But in 2012, what he described as "social anxiety disorder" kicked in, "where your mind takes over and usually goes into the future and sort of predicts what you think is going to happen, and usually it's bad stuff."

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At first, he believed a frightening episode of racing heartbeat was the root cause of trouble. But after winning his third-round 2012 Open match, setting up a fourth-round meeting with Federer, he found his mind so unsettled that he sought psychiatric help in the middle of the night and withdrew from the Federer match.

Now 33, and having been away from major tournament play since that 2012 Open, Fish on Monday returned for one final Grand Slam tournament at Flushing Meadows, with the intent, he said, of "conquering" matters.

He began Monday, in oppressive heat and humidity, by defeating 22-year-old Italian Marco Cecchinato, ranked 106th in the world, 6-7 (5-7), 6-3, 6-1, 6-3. Fish is himself ranked a lowly 581st, given his long absence from the tour. And he admitted he had "spent a lot of time on the court [Monday] telling myself that I'm going to be OK; everything's going to be OK; you're going to be fine. A lot of sort of internal talk."

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When he let slip a chance to serve out the first set at 5-4, and wound up losing the set in a tiebreaker, he began to worry about the muggy heat -- conditions he said he "used to absolutely love."

"But with what I have had to deal with, I was super anxious about the weather," he said. "I knew I was playing fine, but was my body going to hold up? Was I going to hold up?"

Those are the kind of thoughts that elite athletes hardly ever acknowledge, though Fish said he is convinced that other top players experience similar anxiety. A modest crowd of some 2,500 loudly backed Fish throughout his match, an atmosphere he "absolutely" could feel.

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"That's why I wanted this to be my last one. That's the memory that I want to last," he said. "A huge part of it is just coming back here, enjoying the experience of this tournament one last time, and sort of conquering what happened where it was all sort of pulled away from me three years ago."

Fish said he took Monday "as if it was my last match until I won," and now "maybe the next one will be maybe my last match."

It will be against Spain's Feliciano Lopez, the 18th seed.

"I don't take it for granted," Fish said of his victory Monday. "I'm glad I got through it."