Sloane Stephens fought back from a set and a break down to beat Heather Watson 6-7(5) 7-5 6-1 to progress through to the second round of Indian Wells.
Stephens, the 2017 US Open champion, has struggled for form for much of the last three years and has fallen outside of the world's top 50.
She possesses a curiously poor record against the Brit - Watson had won five of their seven meetings, with the pair having last met in the round of 64 at the Miami Masters in 2016.
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Both players traded breaks during an even first set with Stephens struggling to impose her aggressive game and a tie-break followed, with Watson narrowly securing the opening set 7-6 (5).
Stephens appeared to be in trouble when she dropped the opening game of the second set to love after three consecutive unforced errors were followed by a lovely cross-court backhand from Watson.
Yet Stephens broke back in a marathon second game that lasted 18 points, with the British player appearing to struggle physically in the California heat.
However, Watson dug deep and fought hard to cling on, even as Stephens began to find her attacking range, thrice holding serve well in hard-fought games. But the momentum had swung and Stephens claimed a decisive break in the 12th game to send the match to a decider.
The American had found her range as the match entered the third set, racing into a three-game advantage on the back of some fine hitting. And while Watson offered resistance in the fourth game - which ran to 20 points - Stephens secured the double break to put her on the cusp of the second round. She would eventually serve it out in the seventh game of the stanza.

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