Serena Williams made a winning return to the WTA tour but needed three sets to get past Bernarda Pera at the Lexington Open to set up a meeting with her sister Venus.
The No 1 seed, who was last in competitive action at a Fed Cup qualifier in February, lost the first set in Kentucky.
Pera had two opportunities to earn a decisive break against the 23-time Grand Slam winner in the next set, but on both occasions Williams fought back and eventually levelled before she hit top gear to win 4-6 6-4 6-1.
"I wasn't in a good rhythm and I just kept thinking Serena, play like you've been practising," Williams told the official WTA website.
"I knew I could play a little bit better if I just hung in there."
Williams will face sister Venus in the second round and is using this tournament as preparation for the US Open, which begins on August 31.
A straight sets victory later in the day for Venus over Victoria Azarenka by a 6-3 6-3 score saw her book a meeting with her younger sister.
"I didn't know how I was going to feel or how I was going to do, but I really didn't hate the atmosphere," Williams added.
"Being in New York will be a little different because of the massive stadium, but the solo court kind of reminds me of my junior days, so there was something kind of nostalgic about that."
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In Prague, top-seed Simona Halep had to fight hard to advance to the second round by beating unseeded Polana Hercog 6-1 1-6 7-6 (7-3) in her first competitive match since she won the Dubai Championships in February for her 20th career WTA title.
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