Caroline Wozniacki played down concerns over her health after winning through to the US Open final on Friday.
The Danish 10th seed led Peng Shuai 7-6 (7-1) 4-3 when the Chinese world number 39 retired on a hot day in New York.
Cramping led to Peng retiring and she needed a wheelchair to get off Arthur Ashe Stadium post-match.
Wozniacki, the 2009 US Open runner-up, was battling a worry of her own heading into the semi-final.
"I have been in bed. A little bit of a cold the last few days," she said.
"I'm feeling much better now and have another day off tomorrow, so I'll come out firing on Sunday [against Serena Williams]."
Such was her concern, Wozniacki went over and checked on Peng as the 28-year-old fell to her knees while struggling in the heat.
Wozniacki said the players' health was more important than any match.
"It was really hard to watch for me whenever I saw her collapse on the court," she said.
"Tennis is great, but the health is more important. To see her struggling out there, I just wanted to make sure she was OK.
"I got the word that she's OK now and just getting cooled down, so that's great to hear. I'm in the finals, which is obviously great.
"It's been five years for me since my last one here, so I'm extremely happy to be back there."
Wozniacki came into the final grand slam of the year as an outsider on the back of her good form.
She has pushed Williams to three sets in two meetings this year, and hopes she can prove victorious on Sunday.
"When she's on fire, she's hard to beat, but I have had two tough matches against her the last few weeks. I was really close," Wozniacki said.
"Hopefully for me that would be third time's the charm."