Jackson Koivun had never hit a competitive shot as a professional golfer 112 days ago. On Thursday afternoon at Medinah Country Club, the 21-year-old rookie stood 2 up through 12 holes in his Presidents Cup debut, paired with Justin Thomas in one of the tightest opening sessions the biennial event has produced in years. Moments earlier, Sam Burns had birdied the par-4 14th in the marquee match to pull himself and Scottie Scheffler level with Min Woo Lee and Sungjae Im, a swing that squared the projected overall session score at 2.5 points apiece with three matches still playing out on the back nine. Two matches led by the Americans, two by the Internationals, and the anchor pairing was dead even — exactly the kind of nail-biter both captains said they expected from an International side finally deep enough to push back against a heavily favored U.S. team.

A rookie thrown into the fire

No storyline loomed larger over the opening fourballs than Koivun's arrival. The former Auburn star turned pro in June after sweeping every major college golf award and setting an NCAA record with back-to-back rounds of 62. In just his third start as a professional, he won the 3M Open outright, beating world No. 1 Scottie Scheffler by three shots with a tournament-record 25-under total, a run detailed in the Associated Press's account of his rise. That victory, and a captain's pick from Brandt Snedeker, made him the first player without a PGA Tour card to make a U.S. Presidents Cup team since Jordan Spieth in 2013.

Snedeker leaned on veteran leadership to ease the transition, slotting Koivun alongside Thomas for Thursday's opening match against Corey Conners and Nico Echavarria — a pairing PGA Tour's preview of the pairings described as an "Auburn-Alabama combination" built to let the rookie settle in fast. It appears to be working: through 12 holes, Thomas and Koivun were 2 up.

"Justin will do a great job putting his arm around him and show him how USA golf is meant to be played," Snedeker said of the Thomas-Koivun pairing.

Across the property, the other three matches were just as tight. Hideki Matsuyama and Ryo Hisatsune had the Internationals 2 up through 13 over Cameron Young and Xander Schauffele, while Wyndham Clark and Collin Morikawa had the Americans 3 up through 11 against Ryan Fox and Adam Scott. In the anchor match, Tom Kim and Si Woo Kim had the Internationals 1 up through 10 over Chris Gotterup and Patrick Cantlay, according to CBS Sports' live scoring coverage of the session.

The competitive spread reflects a genuinely uncertain week. International captain Geoff Ogilvy, running his first Presidents Cup as skipper, joked about the pressure of setting pairings for the first time, telling reporters Wednesday, "I don't know, it's the first time I've done this." His side has lost eight of the last nine Presidents Cups, but with Matsuyama, the Kim duo and a healthy Fox all delivering points through Thursday's front and back nines, that history looked shakier than usual.

The Presidents Cup runs through Sunday, with the first team to 15.5 points out of a possible 30 claiming the trophy, per tournament format details. Friday's session shifts to foursomes, where Snedeker and Ogilvy will decide whether to keep Thursday's pairings intact or reshuffle based on how the opening fourballs finish. For Koivun, whichever way his debut match ends, the week already marks one of the fastest rises from college fairway to team-competition spotlight the sport has seen.