British number one Johanna Konta had to dig deep to join compatriot Heather Watson in the Miami Open last 16.
Konta, the 24th seed, recovered from a sluggish end to the opening set to beat Russian qualifier Elena Vesnina 4-6 6-1 7-6 (7-3) in two hours and 23 minutes.
The Briton looked to have weathered the storm when she went a break up in the third set but Vesnina fought back.
Konta twice had to serve to stay in the match but held her nerve before taking control of the tie-break.
She will face 32nd seed Monica Niculescu of Romania in the fourth round.