Johanna Konta was given a scare by qualifier Aliaksandra Sasnovich before booking her place in the third round of the Miami Open.
The No 10 seed was pushed all the way by her Belarussian opponent who finally succumbed 6-2 6-7 (5/7) 6-4 after two hours and 40 minutes.
However, it all appeared to be plain sailing for Britain's No 1 when she wrapped up the opening set in just 33 minutes, thanks to two breaks of serve.
In the second, Konta looked in control once again as she moved into a 4-2 lead - and had a point for 5-2 - before the 23-year-old from Minsk staged a brave recovery.
She won seven of the next 10 games - including a tight tie-break during which Sasnovich never trailed - before Konta dug deep in the decider.
After claiming a decisive break in game five, Konta closed the door on the world No 120 and moved into the last 32 where she will face Pauline Parmentier of France.
The match was twice disrupted by rain, including a 30-minute break during the second set tie-break.
Also through are top seed Angelique Kerber and this year's Australian Open runner-up Venus Williams.
Kerber beat Duan Yingying of China 7-6 (7-3) 6-2, with the German having to recover from 3-5 down in the opening set - before winning 10 of the next 13 games.
And the two-time Grand Slam winner from 2016 was unhappy over her treatment by the organisers.
Kerber was originally given a mid-afternoon slot on centre court but, due to weather delays, was moved to one of the outside venues and did not start her match until after 11pm.
She said: "It was tough because it was really windy, the conditions are really tough when you play so late. I was really trying to stay positive and not think too much of the conditions.
"I don't think it was fair moving me but what can I do? It was not my decision but I think it is not really fair to me."
Williams, meanwhile, beat 20-year-old Brazilian Beatriz Haddad Maia 6-4 6-3 in another contest that ended in the early hours.
Despite serving nine double faults, the 36-year-old was always in control and the No 11 seed will now meet the world No 95 from Romania, Patricia Maria Tig.