This was, in just about every measurable way, an up-and-down performance by Serena Williams, filled with double-faults - 10 in all - and two dozen other unforced errors.
With her bid for a calendar Grand Slam at stake, and facing a qualifier ranked only 110th, Williams was far from dominant in the second round of the US Open last night, before pulling ahead and pulling out a 7-6 (5), 6-3 victory over Kiki Bertens.
"Today, I was a little tight," Williams said in her on-court interview. "I think it showed."
She got broken early. She didn't manage to earn a break point against the strong-serving Bertens until the 10th game.
But as the 33-year-old American has demonstrated time and time again during her remarkable career, she can bring out her best when she needs it.
"I know that I can try to make a comeback," Williams said, "or try to make a run for it."
Williams finally roused herself to break back when Bertens served for the first set at 5-4.
Then in the tiebreaker, Williams trailed 4-0, before turning things around, helped by shaky play from her Dutch opponent, who only once has made it to the third round at a major tournament in 14 appearances.
Williams, in contrast, has won the past four major titles, a streak that began at last year's US Open, and 21 overall.
If she can win five more matches at Flushing Meadows - starting in the third round against Bethanie Mattek-Sands in an all-US match-up tomorrow - Williams would complete the first calendar-year Grand Slam since Steffi Graf in 1988.
Meanwhile, defending champion Marin Cilic powered into the third round of the men's event with a 6-2 6-3 7-5 demolition of Russia's Evgeny Donskoy.
US Open, live, Eurosport 3.45/Sky Sports 1 4.0