If this is how Serena Williams serves when she can't practice properly because her right shoulder is sore, watch out when she's 100 percent healthy.

A year after falling two wins short of a calendar-year Grand Slam by bowing out in the U.S. Open semifinals, Williams showed zero signs of shoulder trouble Tuesday night as she began her bid for a record-breaking 23rd major title.

She hit 12 aces and reached 121 mph on her powerful serve during a 6-3, 6-3 victory over Ekaterina Makarova, a potentially tricky first-round opponent at Flushing Meadows.

"I was pleased with my serve, because I haven't been hitting a lot of serves at all," the 34-year-old Williams said. "In practice, none of them were going in, so I was definitely excited about that."

Since equaling Steffi Graf's mark for most Grand Slam singles trophies in the Open era, which dates to 1968, by earning No. 22 at Wimbledon in July, the No. 1-ranked Williams had only entered one event — the Rio de Janeiro Olympics, where she was upset in the third round. She cited a sore shoulder in withdrawing from a hard-court tournament a week later.

Looked perfectly fine against Makarova, a two-time Grand Slam semifinalist who is ranked 29th and beat Williams in straight sets at the 2012 Australian Open.

"I knew today I needed to be focused because I've played her. She's gotten to the semifinals. She goes deep in majors. She knows how to play big matches on big courts. She's not intimidated," Williams said. "I knew I had to really come out today. It was my only option, really."

Well, consider that done.

Wearing black sleeves on each arm — she called the accessories "definitely functional" because they "keep my muscles warm" — Williams averaged 108 mph on first serves and won 17 of the first 20 points she served, 36 of 46 overall, never appearing to be the least bit bothered by anything.

And she even figured maybe the time she couldn't spend serving during training sessions paid off, in a way, because she was forced to work on other aspects of her game, including footwork.

"I couldn't hit any balls. I wanted to stay fit, so ... I guess that kind of helped me out a little bit," she said.

In 2015, Williams arrived at the U.S. Open having won four consecutive major titles for a self-styled "Serena Slam." But had she won the championship in New York, too, she would have made it 4 for 4 within a single season, something no one had done since Graf in 1988.

But that pursuit ended with a surprising semifinal loss to Roberta Vinci of Italy.

Later, Williams acknowledged what was at stake had been a burden.

Williams was asked Tuesday whether this edition of the U.S. Open might be a more pleasant experience than a year ago, without the same sort of history on the line.

"I had a great experience last year. I was going for something that no one has done in a really long time," she replied. "Yeah, it didn't end out wonderful for me, or the way I wanted it to end, but it was all I could do. That's all I could do. If I could make the semis this year, I'd be excited about that."

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