MOSCOW, Idaho (AP) -- Boise State had no reason to worry when Idaho cut the Broncos' lead to four points early in the second half.
After all, Boise State had Ian Johnson.
Johnson scored four touchdowns and rushed for 183 yards as the 15th-ranked Broncos (8-0, 4-0 WAC) beat Idaho 42-26 on Saturday for their eighth straight win and sole possession of first place in the Western Athletic Conference.
Johnson scored three of his touchdowns in the second half, after Idaho (4-4, 3-1) closed within 21-17 early in the third.
"Nobody panicked," said Johnson, who had just 61 yards at halftime. "We said we want to run the ball and whittle the time away."
Johnson scored on runs of 8, 18, 4 and 12 yards, giving him 1,181 yards and 18 touchdowns this season.
Although Johnson weighs just 194 pounds, coach Chris Petersen said he is much stronger than he looks.
"If a guy tries to arm tackle him, he's going to break that," Petersen said. "If we give Ian a chance, he's always going to get positive yards."
Jared Zabransky completed 10 of 22 passes for 145 yards and two touchdowns for the Broncos, who had a tough time with an in-state rival they have beaten eight straight times, usually by lopsided margins.
"It felt like a rivalry," Zabransky said. "We definitely didn't look past these guys.
"We knew they were going to try to smash every hope we have," Zabransky said, referring to the Broncos' quest for a BCS bowl bid.
Idaho, which entered with a share of the conference lead, had a three-game winning streak snapped.
"We have four football games left. We have a chance to have a decent season. That's all I'm worried about," said coach Dennis Erickson, in downplaying the suggestion of a moral victory. "I knew we would compete."
The Vandals were tough on defense in the second half, but failed to score touchdowns in two key situations.
On the first series of the second half, Idaho's Stanley Franks intercepted his seventh pass of the season -- getting a pick for the sixth game in a row -- setting the Vandals up at the Boise State 24. But they settled for Tino Amancio's 29-yard field goal to cut the lead to 21-17.
Johnson replied with an 18-yard touchdown run for Boise State.
Later in the quarter, Idaho's Ryan Davis blocked a punt and Ben Alexander ran it down to the Boise State 26. A face mask penalty gave the Vandals the ball on the 11. But Idaho again had to settle for a field goal, this time a 25-yarder by Amancio, to cut the lead to 28-20 as the third ended.
"I was really proud that we put them (the defense) in a bad situation and they held them to field goals," Petersen said.
Steve Wichman's 41-yard touchdown pass to Marlon Haynes cut the Boise State lead to 28-26 with 7:05 left in the game. Wichman's 2-point conversion pass to Haynes was incomplete.
Rashaun Scott ran the ensuing kickoff back to Idaho's 40, and the Broncos added 15 yards on a late hit penalty against Amancio to take possession at the 25. Johnson ran in from the 4 to give Boise State a 35-26 lead with 5:02 left. He also added a late touchdown.
"It's definitely discouraging when it's right there at your fingertips," Erickson said.
Petersen said his offense had little momentum in the second half until Scott's return.
Wichman threw for 328 yards and three touchdowns, completing 24 of 45 passes.
In the first half, Wichman threw touchdown passes to Wendell Octave and Luke Smith-Anderson for a 14-7 Idaho lead. Zabransky's touchdown passes to Legedu Naanee and Derek Schouman, sandwiched around Johnson's 8-yard scoring run, gave Boise State a 21-14 halftime lead.
Johnson became the first Boise State runner to rush for 1,000 yards since David Mikell in 2003. He is the ninth back in the program's history to break the 1,000 yard barrier.
"That was definitely one of my goals," he said.
Boise State now leads the series 18-17-1. Erickson lost to the Broncos for the first time in five outings.
The Vandals retired the No. 17 worn by former quarterback John Friesz on Saturday. He was a three-time Big Sky Conference player of the year and the 1989 winner of the Walter Payton Award, given to the best player in Division I-AA.