Trailing holders the United States 6-4 after the rain-delayed foursomes were completed earlier, Europe rallied superbly in the two foursomes and four fourballs when play was halted in fading light.
Britons Westwood and Donald, in the top foursomes encounter, were four up on American heavyweights Tiger Woods and Steve Stricker after nine holes.
Woods and Stricker had won their first two matches of the week but, with the world No. 1 struggling for form on Saturday afternoon, the Americans were four over par with their own ball.
"It's a shame it got dark," world No. 8 Donald told reporters after he and Westwood had birdied the first two holes.
""It was great to see so much blue (for Europe) on the board. I think it motivated all of us."
Northern Irishmen Graeme McDowell and Rory McIlroy, who birdied the par-three seventh after McDowell struck his tee shot to four feet, were three up on Zach Johnson and Hunter Mahan after seven holes of their foursomes.
The Europeans, cheered on by jubilant fans, were also in control of the four fourball encounters that were included by organizers in a revamped format for the third session to try to make up for lost time.
Padraig Harrington and Ross Fisher were one up on Jim Furyk and Dustin Johnson after eight holes while Peter Hanson and Miguel Angel Jimenez were two up on Bubba Watson and Jeff Overton after six.
Italian pair Edoardo and Francesco Molinari, the first brothers to be paired together at the Ryder Cup since Charles and Ernest Whitcombe in 1935, were one up on Stewart Cink and Matt Kuchar after five holes.
In the bottom fourball match, Britain's Ian Poulter and German Martin Kaymer were two up on Phil Mickelson and Rickie Fowler after four holes.
The six unfinished matches will resume at 0745 local time (0645 GMT) on Sunday before the 38th Ryder Cup concludes with the 12 singles.
In Madison, Mississippi, Brendon de Jonge and Bill Haas share the second-round lead at the Viking Classic and both are also looking for a win.
The co-leaders are at 12-under 132 after both shot 66s on Friday.
Haas has one victory on the Tour and de Jonge is still looking for his first.
“I’ve been there late on Sunday several times this year,” de Jonge said. “Obviously, I haven’t been able to close the deal, but I’ve definitely had some very good opportunities this year.”
Haas, who won the Bob Hope Classic in a playoff earlier this year, said he would like to add to his experience as a victor.
“I played 160-something events probably, and I’ve won once,” Haas said. “I’m 1 for 160, if you look at it as winning and losing. But it’s difficult out here, so I’m lucky to have done it once.”
De Jonge made his 30th start this year at the Viking Classic. He has finished in the top 10 six times this year. He said his second round Friday was not perfect, but close enough.
“You never want to say it’s an easy round,” he said. “I felt like it could have been a couple better, but I’ll take 66 any time.”
Haas has found the Annandale course friendly in his past two starts here. He finished tied for third in 2007 and tied for fourth in 2008. He is 39 under in 10 rounds at the Viking Classic, all at par-or-better.
Haas credited his putting for keeping him out of trouble in his second consecutive 66 round.
“Yeah, I played solid,” Haas said. “I think I made about a 5-footer on hole No. 4. That’s about the longest putt I’ve had to save par.
“There’s easy holes out there, and there’s hard holes. You’ve got to make sure you par those hard holes.”
Haas said he was surprised at how well he was playing, having taken the past two weeks off.
Michael Allen, winless since joining the Tour in 1984, finished three strokes back after a 6-under 66. Allen is one of eight active players without a win. Nathan Green offset a bogey with five birdies for a 68 on the day, putting him at 9 under through two rounds.
