Now they're opponents.
And the stakes in the Dell Technologies Match Play are personal.
The loser goes home.
The most intriguing match that came out of the draw at the start of the week was packed with significance Thursday when Spieth and Reed won matches for the second straight day to set up a showdown on the skirts of Hill Country in Texas. They play Friday, one of four matches between players who have yet to lose this week at Austin Country Club. Reed fired the first shot when asked what made Spieth a good opponent in match play.
"I don't know. My back still hurts from the last Ryder Cup,'' he said with a laugh, alluding to the way he carried Spieth in their partnership at Hazeltine to a 2-1-1 record in team play during a rare American victory.
Spieth dodged trouble early against Li Haotong, who missed putts inside 8 feet on two of the opening three holes, won the second hole when Spieth hit into the hazard and thought he won the fourth hole until Spieth matched his birdie by chipping in from short of the green.
Spieth never trailed and pulled away with a savvy play on the par-4 13th over the water and into the wind. He hit driver well to the right toward the gallery, which gave him a clear look at the green without having to hit over any of the lake. His pitch-and-run settled a foot away for birdie and a 2-up lead, and Spieth closed him out, 4 and 2.
Right behind was Reed in his match against Charl Schwartzel, and the South African was 2 up at the turn until Reed won the next two holes to set up a tight finish. Schwartzel stayed 1 down when he missed a 5-foot par putt on the 17th. Needing a birdie on the 18th to halve, Schwartzel could only watch as Reed hit a wedge that nearly went in and stopped a few inches away.
Reed and Spieth are 8-1-3 as partners in the Presidents Cup and Ryder Cup. They are 1-1 in PGA Tour playoffs, with Reed hitting through the greens to short birdie range when he won the Wyndham Championship in 2013, and Spieth returning the favor in 2015 at Innisbrook by winning a playoff with a 30-foot putt.
They don't have much of a relationship except in team competitions, and even then it's unusual.
"Because we're so competitive with each other within our own pairing at the Ryder Cup, we want to outdo each other. That's what makes us successful,'' Spieth said. "Tiger says it's a phenomenon. It's not something that he's used to seeing in those team events. Normally you're working together. But we want to beat each other every time. In alternate shot, if we don't win a hole, I want it to be his fault and he wants it to be my fault.
"We've almost played every single match we've been involved in together against each other,'' he said. "We just happen to be wearing the same colors.''
Noren, who has played only 30 holes, has won six of his last seven matches. Thomas can reach No. 1 by winning this World Golf Championship because Dustin Johnson, the defending champion, was among 20 players already mathematically eliminated.
Johnson won seven matches last year. He has lost both his matches this year. Others eliminated were Jon Rahm, last year's runner-up; Zach Johnson; ex-Texas Longhorns Jhonattan Vegas and Dylan Frittelli; and Daniel Berger.
Still alive, but still needing some help, were Rory McIlroy and Phil Mickelson. McIlroy had an easy time beating Vegas, while Brian Harman knocked out Peter Uihlein in the other match in their group. Harman will win the group if he beats McIlroy on Friday; McIlroy has to win to have any chance of making it to the weekend, and it likely would involve a playoff.
"At least I've given myself a chance to progress,'' he said.
Mickelson, who lost to Charles Howell III in the opening round, rallied from 4 down after eight holes and won the last three holes to beat Satoshi Kodaira, who missed putts in the 10-foot range on all of them.
Mickelson is coming off a victory in the last World Golf Championship in Mexico City, and found himself lacking energy and enthusiasm in his loss to Howell, and in fall behind to Kodaira. He attributed it to a bad attitude.
"And you know what happens when you walk with your head down -- animals, they get eaten,'' Mickelson said.
His only hope is to beat Rafa Cabrera Bello and for Howell to lose to Kodaira. Head-to-head matches are not used for tiebreakers, so if that were to happen, Mickelson and Howell would go to a sudden-death playoff. It might feel like that to Spieth and Reed when they get to the first tee.
"He's not going to give you holes,'' Reed said. "You have to go and play some good golf. And that's what it's going to down to. Because I plan on not giving him any holes.''