World number three Coco Gauff was pushed hard by American compatriot Sachia Vickery before overcoming the qualifier 6-3, 4-6, 7-5 at the WTA Stuttgart clay-court tournament on Wednesday.
The US Open champion needed two hours 27 minutes to silence her second round opponent, ranked 134th in the world.
Gauff began brightly, rattling off the first three games, but from then on it was to become an error-strewn struggle.
She double-faulted 15 times, enabling Vickery to get 19 break points, of which she converted seven.
Gauff converted six with the most important one coming in the seventh game of the deciding set.
Trailing 0-2, Vickery fought her way back to take a 4-2 lead, with Gauff then clinching the crucial game on her fourth break point.
Hard-fought battle and total respect
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