By population, the city of San Diego ranks No. 8 in the country, with approximately 1.4 million residents.

By professional sports teams, however, San Diego now ranks perhaps No. 40 in the U.S.

It has baseball’s San Diego Padres … and we are done talking about Big Four U.S. sports teams based in one of the world’s wealthiest and most-livable cities.

Once upon a time, San Diego had an NBA team (the Clippers) and an NFL team (the Chargers), each of which abandoned the city to move to Los Angeles.

Which would seem to leave something of a void for another sports entity to step into, there in San Diego.

Like, say, a major-college athletic program and, particularly, its football team.

Which improved to 4-0 tonight with a victory at Air Force in a wind- and rain-lashed game halted for 88 minutes halfway through the second quarter because of concern about lightning strikes, in Colorado Springs.

Let’s look at what is going on with San Diego State’s football program.

–The Aztecs’ 4-0 start includes victories over Pac-12 stalwarts Arizona State (30-20, on the road) and 19th-ranked Stanford (20-17, in San Diego). Those two victories were responsible for getting San Diego State ranked No. 22 in the nation.

–They are beginning to feel like a team of destiny. They trailed at home to Stanford when the lights went out with less than four minutes to play — but came back to win, after a 22-minute delay, when power was restored. They were down 9-0 to Air Force when lightning forced another break in play, the Aztecs’ second in eight days, and they fought back to a 28-24 victory.

–They have crusty old coach who seems to know what he is doing, in the marvelously named Rocky Long, and a running back, Rashaad Penny, who piles up yards for a run-first team.

–They are conditioning fans to a certain level of success, after several decades of middle-of-the-packdom — with consecutive 11-3 seasons capped by bowl victories. The 4-0 start this year is the school’s best since 1981. And the victory at Air Force? Their first victory while ranked in the national poll since 1977.

–They have a big stadium (54,000 capacity for college football) they no longer have to share with anyone, in San Diego Jack Murphy Stadium. And that stadium is centrally located and a short drive from the campus of San Diego State, enrollment 33,800.

San Diego State football has a lot going for it. Including, in the short term, what looks like a fairly easy schedule for the next couple of weeks (home to Northern Illinois, away to UNLV). Then the Aztecs play host to former Mountain West Conference big dog Boise State.

If they get through those three games, a run at an unbeaten season will come into view, even if looking ahead is often dangerous.

So, the Aztecs are doing what they need to do: Winning.

Now is when we wonder when the city will notice.

According to city figures, San Diego State averaged a modest 25,617 fans through the turnstiles last season, significantly less than the 37,289 per game announced by the school. Significantly less than one would assume could turn out for a top-level college team, in a city of 1.4 million, that was working on another 11-3 season.

The first two home games this season drew 46,132 and 43,040, according to the school, and we probably can safely assume both in-stadium crowds were in the 30,000s.

An issue: San Diego apparently sees itself as a major-league city, rather than as a very big college-football town.

The locals may want to reconsider that mind-set, given that San Diego has declined to one-bigtime-pro-franchise status, along with Green Bay and Portland and Oklahoma City and Jacksonville …

A further issue? San Diego has shown zero appetite for building a new stadium or arena, which would be pretty much required to lure the NFL, NBA or NHL.

Anyway, neither the NBA nor the NFL has plans to expand, nor an existing franchise keen to make a move, even to San Diego and its perfect climate. And the National Hockey League doesn’t seem a good fit.

A Major League Soccer team seems likely, in the next few years, but MLS is not really major league yet, no matter how it refers to itself — and seems unlikely to change that for at least a decade.

After the victory over Air Force, San Diego Union-Tribune columnist Kevin Acee did a piece in which he acknowledged that San Diego State football still has some work to do to prove itself to the city’s sports fans.

“Proof” seeming to consist of continued success, on a weekly basis, as well as a victory or three over college football’s leading powers, if and when they get a shot at them.

It would help, too, if San Diego State played in one of the nation’s five elite college football leagues, but there they are in the Mountain West, meaning they need an unbeaten regular season, as well as lots of stubbed toes among traditional powers, to hope to get into the semifinals of the national-championship tournament.

But, still, what else have you got right now, San Diego?

The Aztecs have never abandoned you, and I’m pretty sure they are not going to move the university to greater Los Angeles.

If the Aztecs continue to thrive (and they are strong in basketball, too), while the Padres continue to stumble, the school’s football team could/should be the hottest sports ticket in the country’s eighth-biggest city.

Instead of sitting around and mourning the loss of the Chargers, why not go see San Diego State play? No need to apologize for following a local team that goes 11-3 and wins a bowl game every year.