At the onset of dusk Friday evening at Stanford Stadium, there was much to be cherished. The vanishing sun brought blessed relief to fans in the sun-baked eastern stands. The field was an immaculate expanse of pure green grass. The band played on, and college football was back.

Exciting, yes, but also a bit troubling. At the stroke of 7:30 p.m., just moments before halftime, Stanford was trailing San Diego State 7-2.

Not exactly what the Cardinal, their fans or the national media could have expected, and that wasn’t the most troubling number of all. Bryce Love, his Heisman Trophy candidacy well documented, had rushed for just 7 yards on 10 carries at that point. You have to read that several times before it becomes even remotely plausible. And it stayed that way for a while.

The fact that Stanford rallied for a 31-10 win was a lot more encouraging to the football program than the sight of a nearly half-empty stadium.

There were legitimate reasons behind this stunning display of apathy (generously tabulated attendance: 40,913). Collegiate games should never be played on a Friday night — that’s the province of high school ball — let alone the long-awaited season opener. Classes don’t begin on campus until Sept. 24, leaving thousands of students many miles away. And the 6 p.m. start was an irritant to folks fearing a traffic snarl and/or awaiting the decency of an afternoon contest.

Still, one could imagine conversations among the FBS bigwigs who lined up this year’s national championship game at Levi’s Stadium (Jan. 7). They’re counting on a hefty representation of Bay Area fans, and judging from the often-tepid crowds at both Stanford and Cal, that simply isn’t going to happen, especially on a Monday night, unless Jim Harbaugh shows up with his Michigan team and promises free, autographed khakis for everyone.

Of far greater concern to Stanford is the fact that Love was shockingly stopped cold by the San Diego State defense for three full quarters — 14 carries, 9 yards — before he broke off a 14-yard run in the fourth. The Cardinal’s offensive line isn’t projected to be quite as strong as it was last year, when Love cranked out 184 yards at San Diego State — including bursts of 51 and 53. But head coach David Shaw takes pride in a relentless running game, simply pounding the ball without mercy, even when the opponent knows what’s coming. Friday night brought a significant blotch in the blueprint.

As it happened, the game-changing turnaround wasn’t about Love, or any aspect of the running game, but quarterback K.J. Costello and his first-class connections with wide receiver JJ Arcega-Whiteside. Costello really came on strong late last season, throwing for nine touchdowns over the final three games against Notre Dame, USC and TCU (the Alamo Bowl), and his offseason hip surgery now seems a distant memory.

Arcega-Whiteside is a marvel, one of the most acrobatic, sure-handed receivers in the country. In the manner of R.C. Owens (as we take 49er fans back a few decades), he catches just about anything thrown to him — just toss it out there and let him work. Costello was drilling strikes for much of the evening, and just when the first half was going down as an incomprehensible bummer, he found his favorite target for a 38-yard touchdown pass that gave Stanford a 9-7 lead in the waning seconds.

That was just the beginning. Costello fired a 19-yard bullet to Arcega-Whiteside for a touchdown on Stanford’s first drive of the third quarter, then found him for an 80-yard score and a two-point conversion that increased the lead to 24-10. Aztecs cornerback Kyree Woods was stride-for-stride in his coverage until he suddenly fell down around the 30-yard line, but the touchdown seemed almost inevitable. Arcega-Whiteside said it all with his body language as he crossed the goal line, vigorously shaking his head as if to say, “They can’t stop me.”

Equally impressive was Stanford’s sharp adjustment against the running game. Juwan Washington, who looks like an able successor to Rashaad Penny in the Aztecs’ scheme, racked up 86 yards in the first quarter but only 72 the rest of the way. Bobby Okereke, forecast to be the next great Stanford linebacker, was all over the field — crisp tackles, a broken-up pass, a sack — and let’s get this annual complaint out of the way early: It’s a bit awkward to have two players wearing the same number, on any roster. Okereke and Love might be the best players on the Stanford team, and they both wear 20. That just can’t happen.

What happens next: a very early Pac-12 opener next Saturday against USC in Palo Alto. Once again, much of the student body will be out of town. And it’s another evening start (5:30). But this is a matchup that never grows old, and count on Love adding precious balance to the passing game. Logic dictates no alternative.

Bruce Jenkins is a San Francisco Chronicle columnist. Email: bjenkins@sfchronicle.com Twitter: @Bruce_Jenkins1