Gehlen (1-1) led 18-11 in the first quarter and kept a six-point lead through halftime, controlling the game 33-27 going into the third quarter.
"We played well the first half. We came out and scored 33 points at half," Gehlen boys head coach Mike Langel said.
But the Rockets (1-0) held the Jays to one point in the third quarter, closing the gap to tie it up at 34-34 going into the fourth.
"We couldn't get the shots to drop," Langel said. "It kind of carried over into the fourth quarter and R-U did a nice job of really picking up the intensity on defense, and we did not handle that well offensively and defensively."
The Gehlen defense gave up a lot of offensive rebounds, allowing R-U second looks at the basket in the third and fourth quarter.
"That really hurt us down the stretch," Langel said.
Gehlen came within two points toward the end, but couldn't retake the lead. R-U claimed the win for their season opener.
The Jays came off a four-overtime game against Trinity Christian the night before.
"I do think a little bit of last night's four overtimes affected us toward the end of the game. We just didn't have any legs left," Langel said. "R-U had a lot of energy, and we were kind of running out."
The Rockets' Tanner Hilbrands was the game's high scorer with 18 points. R-U's Nick Braun scored 11.
Leading scorers for the Jays were Blake Wiltgen with 13 points, Derek Bretey with nine and Colton Kneip and Michael Whitead with eight.
Wiltgen had a double-double night with 10 rebounds and Kneip added 11 for the night.
Wiltgen also nabbed four steals
"They battled. I was pleased with the way they played," Langel said. "R-U played a nice game, so we're looking forward to playing them again."
Gehlen travels to Marcus Friday to meet up with Marcus-Meriden-Cleghorn.