Canada was tied with Spain for third place at 25 under.
The Canadian team of Taylor Pendrith of Richmond Hill, Ont., Corey Conners of Listowel, Ont., and Adam Svensson of Surrey, B.C., came into the day in fifth place. They had a share of the lead after the opening round.
Arizona State junior Jon Rahm had a 62 for Spain to top the individual standings at 18 under, a stroke ahead of DeChambeau.
Sweden was second. Texas Tech sophomore Hannes Ronneblad had a 64, and Marcus Kinhult shot 67.
The top teams will close Saturday on the Iriyama Course.
DeChambeau also birdied five of the first six holes on Karuizawa 72 Golf East's Oshitate Course and had his lone bogey on the par-3 eighth.
Virginia senior Denny McCarthy added a 67 and the 14-time champion Americans set records for best team round at 14-under 128 and three-round total at 31-under 397. Texas sophomore Beau Hossler had a 68, with only the top two scores counting in the team total.
This is the 26th edition of the World Amateur Team Championship, which is held every two years.
In each round, the total of the two lowest scores from each team constitutes the team score for the round. The four-day, 72-hole total is the team’s score for the tournament.