Sydney - Italy's Sara Errani won through at the Sydney International in a match-up against compatriot Roberta Vinci on Sunday, as American teen Madison Keys pulled off an upset win over Simona Halep.
Errani, the third seed and world number seven, said it had been tough playing in the heat in her first-round match against Vinci, her doubles partner, with the first set taking 40 minutes.
"But I like hot weather," she said after her 6-4, 6-2 win.
"The hard thing is not the kind of play because we know each other very well -- it's more playing against your best friend that is very difficult.
"It is not easy to go there and play your best, but I think we played a good match today."
Earlier, rising American star Madison Keys bundled seventh seed Halep out of the tournament 6-1, 6-4 to progress to the second round, where she will face wildcard Ajla Tomljanovic who beat Daniela Hantuchova in straight sets.
Keys made the quarter-finals of the Sydney tournament as a 17-year-old a year ago before she fell to China's Li Na in three sets. But in Halep she faced an opponent struggling to find form and who was down 3-0 early in the first set.
The Romanian staged a recovery in the later half of the second set and fought back from 5-0 down to 5-4, but could not fend off the in-form American.
"She fought to the very end... I was really just trying to focus on playing well and doing what I do well, and I think I did a pretty good job," Keys said.
Croatian wildcard Tomljanovic downed Hantuchova 6-4, 7-5 to progress to the second round.
The Sydney International has five of the top 10 women's players, including defending champion Agnieszka Radwanska and Petra Kvitova, but America's eighth seed Sloane Stephens withdrew on Sunday with a wrist injury.
"I was having some pain in my wrist and the doctor recommended I not play this week," said the world number 12, who had been due to face Russian Svetlana Kuznetsova in the first round.
"This is a difficult decision, but the best decision for me and my team to make."
Kvitova said the field was tough despite the absence of world number one Serena Williams.
"I think it's good to be here competing before the Aussie Open," she said, of the season's first major, starting in Melbourne on January 13.
"I think it's going to be a tough tournament."