With the spotlight firmly on her little sister Serena stalking a calendar year Grand Slam at the U.S. Open, Venus Williams quietly goes about the business of winning like a champion.

Monday, she had to tough out a 2-hour, 45-minute match at Arthur Ashe Stadium against the unseeded and undaunted Monica Puig, winning, 6-4, 6-7 (7), 6-3.

After being up a break in the second set, Williams found herself extended to a tiebreaker as the gritty Puig ran down everything and managed to keep her opponent pinned on the baseline. In their only other meeting in 2013, Puig forced three sets in a loss in Charleston.

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"Yeah, I was a little bit shocked I was still out there," Williams said of being carried to a third set. "I thought I had the match wrapped. She played really good points."

The two-time Open champion, who is 35, and the 85th-ranked player in the world, who is 21, exchanged long rallies during an intense, high-quality match with no timeouts. They then exchanged compliments after it ended.

"I am so excited I had this opportunity," Puig said. "Compared to two years ago, we still had the same fight in a long match. At 35 years old, I hope I am playing that well. She is a great champion, great fighter and one thing nobody can take away from her is all the titles she has to her name. Honestly, I don't care what anybody says about her age or anything else, she's a great champion. In my eyes, a real honor to play her again and hopefully, I can play her a couple more."

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Said Williams: "Give her a lot of credit, too. She had a lot of really good shots at the right moments, so she's a really good competitor."

As for the lack of timeouts, somewhat unusual in a women's match of that length, Puig said: "I just think we are both extremely healthy at the moment. No need for that. It was a match we had no time to let our mind wander away from what was going on. If someone dropped the intensity for even a second, the other one was already reading it."

In other opening matches, Sloane Stephens' comeback season was derailed by fellow American Coco Vandeweghe, 6-4, 6-3. And Eugenie Bouchard's dismal year was brightened by a win over Alison Riske, 6-4, 6-3.

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Stephens had once reached No. 11 in the world without winning a tournament or ever reaching a final. But this summer, she reached the Washington final and won, validating a lot of hard work after a disappointing 2014.

"I was trying my butt off and it just wasn't there," Stephens said. "I mean, I hit some good shots, she hit some better ones. That's kind of how it was."

Bouchard, 21, has plummeted in the rankings after reaching No. 5 last season. She currently is No. 25 and looking down rather than up with 10 opening-round losses this season.

She fought back from a break down in the first set against Riske Monday, an improvement in Grand Slam performance over first-round losses in the French Open and Wimbledon.

"It's great to get one win," Bouchard said. "I'm just focused on one day at time, one point, one match. Not looking ahead at all. Not getting ahead of myself."