Riddick had runs of 55 and 27, the two longest rushes of his career, to pace Notre Dame (7-0), which is off to its best start in a decade and has a big game ahead against No. 10 Oklahoma next week. The Cougars (4-4) fell to 0-3 on the road as they surrendered a season-high 270 yards rushing.
Backup quarterback Tommy Rees, starting in place of injured Everett Golson, completed 6 of 7 passes in the first quarter for 86 yards and a touchdown, throwing four of those to Tyler Eifert. But Rees missed his next seven passes and the Irish attempted only three passes in the second half.
Rees' only completion of the second half was a 31-yard pass to TJ Jones with a little more than a minute left in the third quarter. Riddick ran the ball up the middle for 19 yards to the BYU 5. Three plays later, George Atkinson III scored on an end around, cutting inside BYU safety Joe Sampson for the touchdown to give the Irish the 17-14 lead.
BYU had a chance to regain the lead on the next possession after an Irish penalty. On a third-and-16 from the BYU 10, the Irish stopped BYU quartereback Riley Nelson. But nose guard Louis Nix III was called for grabbing Nelson's face mask.
The Cougars drove to the Notre Dame 31, but Nelson was sacked for a 9 yard loss. Moments earlier Cody Hoffman was wide open for what would have probably been a touchdown, but Nelson's pass wasn't close.
Nelson was 23-of-36 passing for 177 yards with two interceptions and two TD passes.
On Riddick's 55-yard run from the 37-yard line, he ran into a pile at the line of scrimmage, put his hand down to keep his balance and then broke out of the pack before being caught by cornerback Jordan Johnson at the 8-yard line. But the Irish ran three straight running plays for a gain of 1 yard and had to settle for a 24-yard field goal by Kyle Brindza to cut BYU's lead to 14-10 late in the third quarter.
Brigham Young took advantage of Notre Dame mistakes to open a 14-7 halftime lead. After going 17 quarters without giving up an offensive touchdown, Notre Dame gave up two in a span of 2:18. Jamaal Williams set up the first score, rushing for 43 yards on five straight carries. He was thrown to the ground out of bounds on the final 21-yard run and Notre Dame safety Matthias Farley was called for a personal foul.
On third-and-goal, Nelson threw a touchdown pass to Hoffman, who was wide open in the back of the end zone after three Irish defenders covered receiver JD Falslev. That touchdown ended a streak of Notre Dame holding opponents without a touchdown on 11 straight drives into the red zone.
BYU got the ball back three plays later when a pass from Rees bounced off the hands of DaVaris Daniels, deflected up and was intercepted by Kyle Van Noy, who returned the ball to the Notre Dame 30. After Notre linebacker Daniel Spond was called for holding, Riley ran the ball for an 8-yard gain to the Notre Dame 12. After a 10-yard pass to Ross Apo, Nelson then threw a 2-yard TD pass that Kaneakua Friel caught as he went to the ground.
Notre Dame had a chance to tie the score late in the half after Riddick's 27-yard run, breaking two tackles and carrying three BYU defenders for the final 10 yards to the BYU 14. But the drive stalled and Brindza missed a 28-yard field goal wide right. He missed a 40-yard field goal on Notre Dame's opening drive of the game.
Notre Dame dominated the first quarter statistically, outgaining the Cougars 120 yards to 40, but led only 7-0. The Irish scored on Rees' 4-yard TD pass to Tyler Eifert.