LAS CRUCES, N.M. (AP) -Boise State knows there's no margin for error in its long-shot mission to land an at-large BCS bid.

The No. 18 Broncos were far from perfect Sunday night against New Mexico State, but good enough to make sure they stayed in the BCS picture.

Ian Johnson scored four first-half touchdowns and ran for 192 yards and Boise State toasted its debut in the BCS standings with a 40-28 win over the Aggies.

''The bull's-eye continues to grow the more we win. We've known that from the start,'' Broncos coach Chris Petersen said.

The Broncos (7-0, 3-0 WAC) earlier in the day landed at No. 15 in the first BCS standings of the season. They were solid offensively, but shaky on defense against the Aggies, who have lost 17 straight games against Division I-A opponents.

Petersen has refused to talk about the BCS and nothing changed after the less than impressive win Sunday over a school that has had just four winning seasons since 1967.

''Zero. I don't have any reaction,'' Petersen said when asked about his team's standing in the BCS lineup. ''It means nothing to me. I have no reaction to that because if one game we don't take care of business, we're not even having this conversation.''

Johnson scored on touchdown runs of 7, 1, 3 and 17 yards and the Broncos finally put away the pesky, pass-happy Aggies with a pair of touchdown passes from Jared Zabransky in the second half.

Afterward, Johnson conceded it was not one of the Broncos' better efforts.

''We went out there and made a lot of mistakes. We made a bunch of stupid mistakes,'' Johnson said.

New Mexico State (2-4, 0-2) kept it close behind sophomore quarterback Chase Holbrook , the nation's total offense leader. Holbrook completed a school-record 49 of 65 passes for 526 yards. He came up 20 yards short of the single-game NMSU record of 546 yards set by Cody Ledbetter against UNLV in 1995.

Holbrook threw two touchdown passes, including a 65-yarder to Derek Dubois in the first half. Holbrook scored on a 1-yard run with 9:19 left in the third quarter that cut Boise State's lead to 27-21 and kept the Broncos' defense guessing - usually wrong - most of the night.

''I felt like our defense was playing on their heels and not playing the type of game that we like to play,'' Petersen said. ''We usually like to come after our opponents and challenge them.''

After Holbrook's rushing TD, the Broncos drove to the NMSU 36 and faced a fourth-and-6. Zabransky threw incomplete but Tim McManigal was called for roughing Zabransky. Four plays later, Zabransky hit Jeremy Childs with a 22-yard TD pass. Big in that 84-yard drive were a 19-yard pass from Zabransky to Jerard Rabb on third-and-10 from the Boise 17 and Zabransky's 24-yard pass to Legedu Naanee to the New Mexico State 40.

New Mexico State coach Hal Mumme said the roughing call was huge.

''We had them stopped at that time and we had the momentum and that was really unfortunate for us,'' Mumme said.

The Aggies still had some fight left and Holbrook completed six passes in a drive that reached the Boise State 13. On fourth down, Matt Pratt 's 30-yard field goal attempt was blocked. The Broncos took over and needed just six plays to score on a 33-yard pass from Zabransky to Vinny Perretta for a 40-21 lead with 13:13 left in the game.

Holbrook completed 11 straight passes in an 82-yard drive in the second quarter that ended with Jeremiah Williams ' 3-yard TD run. Holbrook's 65-yard pass to Dubois came with 1:27 left in the first half.

Dubois caught the ball near the Boise State 30 as two Broncos collided trying to break it up and Dubois scooted away untouched. The drive began after Zabransky fumbled a pitch at the NMSU 18 and Aggies safety Derrick Richardson recovered it.

Holbrook ran his streak of completions to 16 straight and had the Aggies at the Boise 24 in the final minute of the first half. The scoring threat ended when Marty Tadman intercepted Holbrook's pass in the end zone on the final play of the half.

The Aggies, whose two wins this season were against Division I-AA Southeastern Louisiana and Texas Southern, riddled the WAC's best defense. Receiver Chris Williams had career highs of 13 catches for 191 yards and Dubois caught six passes for 124 yards.

Zabransky was 14-of-21 passing for 215 yards.