Come Sunday morning, BYU's humbled football team was still trying to understand what went wrong in the gloom and fog of San Diego's Jack Murphy Stadium Saturday.

BYU was drilled by San Diego State 27-15, an outcome that no one saw coming.On the one hand there were the Aztecs, riding a 6-game losing streak, owners of a 1-7 record and one of the nation's 10 worst defenses; on the other hand there were the Cougars, riding a 7-game win streak, owners of a 7-1 record and an offense and defense among the nation's top 10.

So what happens? The Aztecs, who had been outscored 108-24 in the first quarter this season, take a 24-3 halftime lead and coast to victory. It marked the first time since 1981 that the Aztecs have defeated a Top 20 team - and the Cougars helped them do it. The Aztecs scored all three of their touchdowns in the first half without traveling farther than 28 yards to the end zone. They intercepted a pass at the BYU 24 yard-line, recovered a fumble at the BYU 28, returned a kickoff 82 yards to the BYU 12, and that accounted for all of their TDs.

"My worst fear became reality tonight," said BYU Coach LaVell Edwards. "We didn't play well at all. We were flat."

Indeed. Sure, the Aztecs were primed to beat the Cougars, a team they loathe for many reasons (numerous lopsided defeats, the '79 national TV debacle, BYU's league dominance, the Doug Scovil years, the Todd Santos snub), but the Cougars see this almost everywhere they go these days (Utah, Hawaii, Wyoming all feel the same way).

A simple case of homefield advantage, you say? Bunk. What's so advantageous about 21,825 fans, the most vocal of which were cheering for the Cougars. Then again, it was only the second time in two months that BYU has played on the road. In all three of their road games this season (Wyoming, Hawaii and San Diego), the Cougars have failed to play well. In both of their losses, to Wyoming and SDS, they showed up flat and were plagued by sacks and turnovers.

On Saturday night, the Cougars allowed the Aztecs to sack their quarterbacks eight times - which, incredibly, nearly equaled the Aztecs' total for the entire season (11). Once again, the Cougars demontrated an inability to handle the blitz, which the Aztecs (not to mention Wyoming and Hawaii) used frequently and successfully. The Cougars no longer seem capable of beating the blitz the way they once did, with hot reads, short dumpoffs, screens, etc.

"We didn't beat them, we kicked their . . .," said linebacker John Wessleman. "They were never in it. We knew their linemen were big and slow. And our down linemen were much quicker. This is the best defensive game we've played in two years."

"I was surprised how much pressure we got on (quarterback Sean) Covey," said SDS Coach Denny Stolz.

The Cougars, who outgained the Aztecs 392-305, also committed four turnovers - 1 interception and 3 fumbles - which not only set up a couple of touchdowns but cost them one touchdown as well, coming as it did on the goal line.

Contrary to what was believed earlier in the week, the Cougars were banged up for Saturday night's game, which certainly didn't help their performance. Because of injuries, linebacker Regan Hansen didn't play until the second half and tight ends Darren Handley and Travis McBeth and running back Mike O'Brien didn't play at all. Covey, who missed the previous week's game with a knee injury, reinjured the knee in the second quarter Saturday night and didn't return to the game until late in the third quarter.

In the meantime, he was relieved by freshman Ty Detmer, who wilted under the pass rush and threw an interception and lost a fumble. Detmer completed 6 of 13 passes for 45 yards and 1 interception.

Covey was noticeably sharper than Detmer. He completed 19 of 32 passes for 279 yards, 1 TD and 0 interceptions, but his comeback hopes were undone by Matt Bellini's goal-line fumble and the Aztec rush.

"I'm very disappointed," said Covey. "We let them get ahead and we lost our composure."

Well, the defense did finally settle down in the second half, led by Bob Davis, the superb junior inside linebacker, who had 15 tackles.