How different would Mariano Rivera’s career have been if baseball’s all-time saves leader had mastered what Mel Stottlemyre was teaching in the spring of 1996?

In his first year as Joe Torre’s pitching coach, Stottlemyre was doing his job when he tried to add off-speed pitches to Rivera’s explosive fastball.

“We didn’t know what we had but the fastball, and we wanted to work on a curveball and changeup,’’ Stottlemyre said before the Yankees’ 4-1 loss to the Mariners Friday night at Safeco Field.

“By the next year, he shelved it,’’ said Stottlemyre, the Yankees’ pitching coach from 1996 to 2005. “His fastball was so good the catchers forgot to call anything else. His curveball had break. And the changeup was decent, but he didn’t throw it with good command. We didn’t tell him not to use them, but the other pitch was so good in crucial game situations.”

Joe Girardi remembers a game in the middle of the 1998 season on July 18 at Toronto when Rivera still toyed with a slider. Rivera had one and a half seasons of being John Wetteland’s replacement as the closer under his belt.

“We had a big lead and he had been working on a slider and he tried to throw a slider to Mike Stanley and he hit a home run. That was the end of the experiment,” said Girardi, who called for the last slider Rivera ever threw in a game.

“We were up 9-1 or 10-1 and he hadn’t worked in five or six days, so I said, ‘Let’s throw some sliders and see what happens.’ He gave up a homer and that was the end of it.”

Girardi remembers Stottlemyre and others attempting to add other pitches to a fastball that in the early days of closing was not always a cutter.

“They always tried, but his fastball was so good he didn’t need it,’’ Girardi said.

Asked how good his changeup, curveball and slider were, Rivera made a sour face and delivered a short but perfect answer.