Korda, a six-time LPGA winner this season, and Allisen Corpuz rallied for a crucial 1-up victory over Spain's Carlota Ciganda and Dane Emily Pedersen to split the early points 2-2 entering Saturday's afternoon four-ball matches at Robert Trent Jones Golf Club.
"We've got world number one and it's very helpful when she plays well," US captain Stacy Lewis said.
Korda and Corpuz became the first duo to win four consecutive Cup foursomes matches, going perfect last year in Spain and this week.
"Nelly was playing really solid all day," Corpuz said. "Every single time you play with Nelly it's like it's going to turn around at some point, just be patient."
Added Korda: "She said I played great today, but she did as well, and we make a really good team."
The Americans seized a four-point edge Friday by going 3-1 in foursomes and four-balls and moved closer to their first Cup win since 2017 with holders Europe needing a fightback in four-balls and Sunday's 12 final singles matches to take the trophy for a fourth consecutive time.
"You can see it," Lewis said. "That finish got us some momentum back."
Korda, who has never played on a US Cup winner, and Corpuz dropped two of the first three holes but rallied on the back nine as Korda improved to four wins and a draw from nine matches where she has trailed by two or more holes.
Korda sank a seven-foot birdie putt to win 10 and a European bogey at 13 squared the match. Korda sank a 20-foot eagle putt with a right fist pump to win the 14th for the first US lead.
A US bogey at 15 knotted the match again but Pedersen missed a par putt to drop the 17th and the last was halved.
Lauren Coughlin, who won her first LPGA titles at July's Canadian Open and August's Scottish Open, improved to 3-0 to equal the best US rookie start with a 4&3 win alongside Lexi Thompson over England's Georgia Hall and Sweden's Maja Stark in which they never trailed.
"It has been incredible," Coughlin said. "It has been awesome and I've been enjoying every minute."
Europe earned a session split as Sweden's Anna Nordqvist and France's Celine Boutier beat second-ranked Lilia Vu and Sarah Schmelzel 4&3. The US duo opened with five straight bogeys to fall 4-down and never recovered.
"It's nice to see some blue on the board," Nordqvist said. "We've just got to keep doing our best."
The other European win was a 1-up thriller by Germany's Esther Henseleit and England's Charley Hull over Ally Ewing and Jennifer Kupcho. Henseleit's approach landed inches from the hole at 18 as they took the last to win.
"Esther just completely stiffed it to half a foot, so I was thankful for that," Hull said.
Noisy fans filled the first-tee stands at the start after more buses averted a repeat of Friday's hours-long waits for spectators to reach the course from parking areas.
