TORONTO -- New York Yankees starter Luis Severino took a massive step forward Friday in his return from the shoulder and back troubles that have sidelined him since spring training.

For the first time since he was a surprise pregame scratch in an early-March Grapefruit League outing, Severino threw off a pitcher's mound. It was an important step for Severino, whose recovery has been marred by setbacks that occurred before he could throw off a mound again.

"Better than I expected," Severino said of his 23-pitch rehab session. "I was expecting my secondary pitches to be a little bit off, but everything was good."

Although he mostly hummed fastballs during the session inside Rogers Centre's visitors bullpen, Severino said he also threw two sliders and a couple of changeups. Each of his pitches was "pretty normal," he added.

Yankees pitching coach Larry Rothschild and manager Aaron Boone were among those paying close attention to Severino's workout.

"Thought he looked really good," Boone said. "The ball was coming out really well. It's obviously a day we've all been looking forward to; certainly he has, as he's felt really good these last couple of weeks. So it's a good step for him."

Severino's bullpen session came on the same day Boone reaffirmed that catcher Gary Sanchez would be back in the lineup Saturday for the third game of the series against the Blue Jays. Sanchez, who has been on the 10-day injured list since July 24 because of a left groin strain, arrived in Toronto on Friday afternoon following a two-game rehab stint at Triple-A.

Severino, 25, originally went on the IL during spring training with a right shoulder injury. About a month after he was first sidelined, he was slated to ramp up his rehab to the point that he would pitch off a mound. That didn't happen. He couldn't quite get comfortable enough to let his pitches fly as he normally would.

A subsequent MRI revealed Severino had a right latissimus strain. It remains a mystery whether that injury was present when he first hurt his shoulder, or if it popped up during his flat-ground throwing regimen in the weeks after he first went on the IL.

Since the lat strain diagnosis, Severino has slowly worked his way back through rest, treatments and a throwing program.

"It's been a really, really long year," Severino said.

With about seven weeks left in the regular season, Severino still believes he will have enough time to get himself fully stretched out to return to the Yankees' starting rotation. Boone said in order for that to happen, the Yankees might end up using some of his big league outings next month as the spring training the right-hander didn't receive.

"You can build him up in September," Boone said. "Let's say he joins us in a few weeks, and gradually we can build him up in the month of September, like we would during spring training. So if he gets to us and he's in a two- or three-inning [work]load, then next time, you can build his pitches and do it in the big leagues."

Boone quickly added, though: "Whether we do that still remains to be seen."

What the Yankees do know, however, is that Severino will have another bullpen session Monday. After taking about two days off, he'll have another one. Severino believes that after about three or four bullpen sessions, he'll start to face live batters in a simulated setting. Once he gets past that phase, he could make a rehab start or two at the minor leagues before joining the big league roster for the first time this year.

"I'm going to help my team in a couple of weeks," Severino said.

Still regarded as the ace of the Yankees' staff, Severino went 19-8 with a 3.39 ERA last season. The two-time All-Star has recorded 200 or more strikeouts in each of his past two seasons.

One injured player who will be looking to help his team Saturday is Sanchez, who suffered his groin injury in late July while running out a ground ball. Twice last season he landed on the disabled list because of right groin strains.

Although Sanchez scuffled a bit at the plate in the two weeks before his injury, Boone is anticipating the catcher will get back to the power-hitting ways that have led him to slugging 24 home runs this season.

"Over time, he's going to be a force for us," Boone said.