You wouldn’t know it by the end result, but Pat Haden’s last pass as a USC quarterback was neither straight nor true.

Fired under duress, it sailed low and wobbly.

“It was,” Haden volunteers, “a terrible throw.”

Shelton Diggs caught it anyway.

Diving to fetch it before it hit the turf, clutching it to his chest in the end zone and raising the ball above his head in celebration, Diggs turned it from underthrown to unforgettable.

The flanker’s game-winning catch gave USC a gutsy two-point conversion, an 18-17 victory over Ohio State in the 1975 Rose Bowl and a share of the national championship.

And, not least, it earned the unassuming Diggs an honorable and unassailable post in Trojans football lore.

“That’s my little claim to fame, that catch right there,” Diggs acknowledges. “I didn’t think about it then, and I don’t think about it a lot now, but it’s nice to know I did something to help USC win a national championship.”

The clutch completion, Haden notes, was “95% catch.”

Diggs considers his former teammate’s assessment and grins.

“That’s probably true,” he says.

Recently retired after a 29-year career in law enforcement, Diggs says he arrived at USC from San Bernardino High in 1973 hoping to become the next great Trojans tailback.

But John McKay and his staff had other ideas. They moved the 6-foot-1, 190-pound Diggs, a sprinter, long jumper, high jumper and all-league basketball player in high school, to wide receiver.

“I wanted to be a running back, but they told me, ‘We always put our best athlete at the flanker spot,’” Diggs, 55, says during an interview at his home near Hesperia. “They said, ‘You can run the ball some on reverses, we’ll throw to you, you’ll block.’”

In 1974, when Diggs replaced recently graduated All-American Lynn Swann as the Trojans’ starting flanker, McKay told reporters that the position was in capable hands. Diggs, McKay noted, “has as much ability as Lynn Swann and Swann was the best flanker we ever had. In fact, Diggs could be better.”

Diggs, however, was no Swann. Beset by shoulder and other injuries, he never lived up to the hype until his senior year, when he led the Trojans with 37 receptions for 655 yards.

In the NFL, he lasted only one season, carrying the ball once for 16 yards, catching no passes and mostly playing on special teams in seven games with the New York Jets in 1977.

“I would have thought I’d do a lot more,” says Diggs, whose three sons — Shelton, A.J. and Ryan — all played college basketball, A.J. at California and his brothers at Western Washington. “It’s disappointing, but I don’t walk around thinking about it on a daily basis. It doesn’t make or break my day.

“That was a long time ago.”

So was Jan. 1, 1975, but USC fans haven’t forgotten.

The fourth-ranked Trojans trailed Woody Hayes’ second-ranked Buckeyes, 17-10, before Haden and J.K. McKay, the coach’s son and Haden’s favorite target, hooked up on a 38-yard touchdown pass with slightly more than two minutes to play.

“I hadn’t done a whole lot that whole game,” says Diggs, who hadn’t caught a pass to that point. “They may have thrown one pass to me the whole game. I was more of a decoy.”

After McKay scored, Diggs says, “I’m running off the field. We’re going to kick the extra point, right? And they’re like, ‘Get back out there. We’re going for two. We’re going to win this thing.’”

Eight years earlier, in the 1967 Rose Bowl, the Trojans had gone for two after scoring a late touchdown against Purdue, only to have a pass intercepted. They lost, 14-13.

This time, Haden took the snap and rolled to his right.

“I actually had decided to run,” the former quarterback says, “and then I realized I was not going to make it. All I saw was a red jersey; I didn’t know who it was, John or Shelton.”

Actually, both were in the back of the end zone midway between the goal post and the far right corner, Diggs slightly in front of McKay, when Haden unloaded the ball.

“I believe I was pretty much uncovered,” Diggs says. “That area of the field kind of opened up and I saw him put the ball in the air. I knew I could get it, so I laid out.”

He pauses.

Sheepishly, he adds, “It was one of my greatest catches.”

In the aftermath, Diggs says, offensive linemen Marvin Powell and Donnie Hickman ran over to congratulate him.

“And Marvin said, ‘Hey D, you know you just made history,’” Diggs says, smiling. “It didn’t really hit me until that moment. I was just trying to make a play.”

After top-ranked Alabama lost to Notre Dame later that night in the Orange Bowl, USC jumped to No. 1 in the final United Press International rankings, claiming a national title that would have gone to Ohio State if Diggs hadn’t made the catch of his life.

Thirty-five years later, Diggs is still asked about it.

And not only by USC fans.

“I’ll have Ohio State fans come up to me,” he says, “and they’ll say, ‘You cost me money with that catch.’”

His knowing smile tells them how little he cares.

jerome.crowe@latimes.com