Clubhouse leader Brenden O'Reilly (USGA photo)

Play was suspended at 8:27 p.m. EDT due to darkness with half of the 156-player field still on the course, including first-round leaders Victor Hovland, 17, of Norway, and Won Jun Lee, 17, of the Republic of Korea.

The championship was delayed twice in the afternoon due to rain and lightning for a total of 4 hours, 51 minutes. The second round of stroke play is scheduled to resume on Wednesday morning at 7:30 a.m., with the first round of match play to follow.

The U.S. Junior Amateur consists of 36 holes of stroke play followed by six rounds of match play, with the championship scheduled to conclude with a 36-hole final on Saturday, July 25, starting at 7 a.m. EDT.

The U.S. Junior Amateur is one of 13 national championships conducted annually by the United States Golf Association, 10 of which are strictly for amateurs.

O’Reilly, who is playing in his first USGA championship, birdied four of his first 10 holes. He struck a wedge to within 12 feet on the par-5 second and then sank an 8-foot putt on the following hole for another birdie. He made putts of 14 and 30 feet, respectively on holes 9 and 10 to get to 5 under overall before he made his lone bogey of the day on the par-5 11th.

“Today, I was a little more aggressive,” said O’Reilly, who won the 2013 Illinois State Boys’ Junior and finished third at this year’s Class 3A state championship. “I had a better strategy for the course and a better game plan. I executed on a couple of more putts.”

Reese Ramsey, 16, of Austin, Texas, was one stroke behind O’Reilly at 3-under 141 after shooting 70 in oppressive conditions in which temperatures soared into the high 90s and the heat index reached 110. He birdied three consecutive holes on the inward nine to erase a double bogey on No. 11.

Sahith Theegala, 17, of Chino Hills, Calif., and Brody Blackmon, 17, of Sulphur Springs, Texas, also reached 5 under for the championship before falling back to 2-under 142. Theegala birdied the first hole, his 10th of the day, before making three bogeys for a second-round 72.

“I am not too disappointed,” said Theegala, who advanced to the Round of 16 in 2014 and the Round of 32 the previous year. “I could have shot 50 on that front nine (his inward nine). I made a lot of putts. I scraped it around.”

Blackmon, the grandson of 1969 U.S. Open champion Orville Moody, birdied two of the first four holes. However, he lost momentum when he missed a 4-foot par putt on the ninth and finished with bogeys on Nos. 16 and 18 for a second-round 73.

“I got off to a hot start,” Blackmon said. “After that, it was a grind. I started missing fairways. Some of the birdie holes, let’s just say I turned into par holes.”

Andy Zhang, who is competing in his fourth U.S. Junior Amateur and was a quarterfinalist last year, used a hot putter to regroup from a tough start and shoot a 2-under 70 for a two-round score of 142. Following a string of three straight bogeys, he reeled off four consecutive birdies to close out the outward nine. He hit an 8-iron to within 9 feet on the par-3 sixth and holed a 16-foot putt on No. 9. He added birdie putts of 25 and 30 feet, respectively, on holes 15 and 16.

“Once I got on a roll, I just kept making putts,” said Zhang, who saved his round on No. 18 when he nearly pulled his tee shot into the water hazard but recovered to make a 5-foot par putt. “If you put it in the right position it is very scoreable.”

When stroke play is completed on Wednesday, the field will be reduced to the low 64 scorers for match play. Theegala, who is playing in his third Junior Amateur, knows the competition will be much different for those in the bracket.

“You cannot force it,” he said. “You might want to make birdies, but if you hit the middle of the fairway, center of the green and make par it’s going to put pressure on your opponent.”

View results for U.S. Junior Amateur