Baltacha won in three sets against Austria's Sybille Bammer
Britain's Elena Baltacha recovered from what looked like certain defeat to beat Austria's Sybille Bammer 3-6 7-6 7-6 at the Sony Ericsson Open in Miami.
Baltacha squared the first-round match at one set apiece but found herself trailing Bammer 4-1 in the final set.
But the British number one had to win four games in succession to force a final set tie-break and then prevail.
Baltacha, ranked 74 in the world, faces a second-round clash against Czech Klara Zakopalova, who is seeded 32.
"I can't believe I'm still part of the tournament," Baltacha admitted after her victory.
"In the third set I was down and I just wasn't executing my shots and gave her some freebies. But then I got stuck in and somehow I managed to pull off the win.
"I think it showed that you have to fight until the very last point. It tells me that mentally I'm very solid now."
Baltacha added: "I played Zakopalova a couple of weeks ago in Doha and she played out of her skin. I think I only won three games.
"Hopefully she won't be able to do that again, she was on fire. I will hang in there, get stuck in and hopefully revenge will be sweet."
Baltacha's fellow Briton Heather Watson was less successful in Miami, losing 7-5 6-2 against Japan's Ayumi Morita to exit at the first stage.
British number two Anne Keothavong failed to make the main draw of the tournament after she was beaten in qualifying on Monday.
Keothavong put on a decent showing in the first set but went down 6-4 6-0 to Anastasia Pivovarova.
Australian Jelena Dokic did qualify after beating German Tatjana Malek 5-7 6-3 6-4 while Jill Craybas went down 6-3 5-7 6-1 to Lauren Davis.
Defending champion Kim Clijsters
and top seed Caroline Wozniacki both have byes to the second round, but world number nine Venus Williams, who lives nearby and considers it her home tournament, was
forced to pull out last week
because of an abdominal injury.
Williams was beaten by Clijsters in the 2010 final but won the tournament in 1998, 1999 and 2001.