The U.S. Olympic Eventing team, from left: Clark Montgomery, Lauren Kieffer, Phillip Dutton, Boyd Martin and coach David O’Connor. (Diane Bondareff/AP Images For U.S. Olympic Equestrian Teams)

Under the beating Virginia sun, Clark Montgomery sat atop his horse, Loughan Glen . When Montgomery and his Irish Sport Horse gelding went into the arena for dressage, the temperature was at 89 degrees, though it felt 10 degrees warmer. In a wool coat, the busy day of eventing at the Great Meadow International felt warmer still.

Montgomery — who will represent the United States in the Olympics next month — posted the best dressage score of the day in that scorching heat, 5.1 points lower than that of reserve Olympian Maya Black aboard Doesn’t Play Fair. After the show jumping round, the two remained at the top of the leader board with the same point differential.

Montgomery said he was proud of the way Loughan Glen handled the heat. But Montgomery, who lives and trains in England’s Cotswolds region, wasn’t as keen on the weather himself.

“I’m hot as hell,” Montgomery said after dressage. “I think my face is still red. It’s hot. It’s really hot. I was looking forward to getting into the sun, but this is a little extreme.”

By the time Montgomery entered the arena for show jumping, the temperature had dropped by three degrees amid a cool breeze.

The show jumping went smoothly; 18 riders, including Montgomery and Black, completed their rounds with no penalties.

“I don’t know what the deal is with me today, but I’m more nervous for this event in front of all you guys than any of my past ones for a while now,” Montgomery said after show jumping. “[Loughan Glen] went in and jumped great. An arena and footing like this is amazing. . . . I couldn’t be happier to be where I am right now.”

Forty horses and their riders took part in the first day of eventing — the equestrian event that includes competitions in dressage, show jumping and cross-country. The last outing for the U.S. team before Rio, it also serves as part of the Nations Cup series, the first such event outside of Europe this year. Joining the Americans for this Cup competition are Canada and Britain.

Through two phases, the U.S. team led with 132.3 points. Team Canada was second (157.2) and Britain third (171.7). The best riders in the team competition were Montgomery, Jessica Phoenix of Canada and Phillip Dutton of the United States.

The U.S. team advanced its lead during show jumping; three of the four American team riders cleared their round, while only two Canadians and one Briton did the same.

Even though eventing is an individual sport, the riders participating in the Nations Cup appreciate the camaraderie.

“The competition, usually you’re an individual,” Britain’s Jodie Amos said. “And the whole team ethic is something that’s really nice to be part of. You do go into it thinking a little bit differently. . . . Everyone’s very supportive of each other.”

The third and final phase, cross-country, begins Sunday morning at 9:30.