NEW YORK — Serena Williams' serve was in fine form in a routine first-round win over Ekaterina Makarova at the U.S. Open on Tuesday
The top-seeded Williams had played just three singles matches since Wimbledon because of a sore right shoulder, but it didn't show as she hit 12 aces, with only one double-fault, in a 6-3, 6-3 victory in 63 minutes.
It was a potentially tricky draw for Williams as she opened her bid for a record 23rd major title. Makarova is a two-time Grand Slam semifinalist who just missed a seed.
"I knew 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.
Williams' first serve averaged 108 mph, and she hit one as hard as 121 mph.
"I was pleased with my serve, because I haven't been hitting a lot of serves at all," she said. "In practice, none of them were going in."
Her sister Venus Williams won her 18th first-round match at the U.S. Open, beating Kateryna Kozlova 6-2, 5-7, 6-4 despite 63 unforced errors. Williams led 5-2 in the third set, but Kozlova. 22, pushed her to the limit in the 2-hour, 42-minute match.
Venus next faces Julia Georges.
"It was great to be challenged and to be pushed," Venus said, "because I had to get in those situations that you know you're going to face in the tournament."
Ana Ivanovic was searching for answers after getting eliminated in the first round for the second straight year. She had seven double-faults and 41 unforced errors in a 7-6 (7-4), 6-1 loss to 89th-ranked Denisa Allertova.
Ivanovic made it to the U.S. Open quarterfinals in 2012, but it has been a steady decline since then at Flushing Meadows.
"I feel like I have been putting a lot of work on the court and in the gym over the year," she said. "It's been very frustrating not getting anything in return."
Ivanovic, who turns 29 in November, said she's not considering retirement.
In men's play, American Jared Donaldson, 19, upset 12th-seeded David Goffin for his first career win over a top-30 player. The qualifier won 4-6, 7-5, 6-4, 6-0 for his first victory at a major.
Juan Martin del Potro, the 2009 champ, beat beat Diego Schwartzman 6-4, 6-4, 7-6 (7-3) after missing the tournament the last two years because of three left wrist surgeries.
Del Potro is ranked 142nd and needed a wild card to get in. But he proved with his unexpected silver medal at the Olympics that he can contend again.
American Steve Johnson rallied to advance. The 19th seed outlasted Evgeny Donskoy 4-6, 1-6, 7-6 (7-2), 6-3, 6-3 in 3:13.
TOMIC outburst: Bernard Tomic muttered at a heckler during his match, making a lewd comment. Tomic said after his first-round loss that he apologized to the fan. "He definitely baited me the whole set for me to say that. But I do apologize if there were people around that heard." The 17th-seeded Tomic lost 6-4, 6-3, 4-6, 7-6 (7-0) to 72nd-ranked Damir Dzumhur.