Two-time champion Venus Williams was pushed all the way by world number 135 Viktoria Kuzmova before reaching the second round of the US Open.
The 37-year-old American took her second match point on teenager Kuzmova’s serve to win 6-3 3-6 6-2.
Williams has seven Grand Slam singles titles, while Kuzmova was making her main-draw debut at tour level.
Meantime, two-time finalist Caroline Wozniacki beat Mihaela Buzarnescu 6-1 7-5 to reach round two.
The Dane will face Russian Ekaterina Makarova next.
“I didn’t do a lot wrong, she just just stepped it up,” said Williams, who is aiming for her first major since 2008 and plays France’s Oceane Dodin on Wednesday.