PORT ST. LUCIE, Fla. -- After a strong showing in his Grapefruit League debut on Sunday afternoon, Nationals reliever Sean Doolittle joked about setting the bar too high for himself.

Doolittle pitched a scoreless fourth inning in the Nationals' 3-1 loss to the Mets at Clover Park, allowing a bloop hit and striking out two on 15 pitches (10 strikes).

"It usually takes me weeks in camp to get swings and misses on my fastball," said Doolittle, whose offering showed late life and zip. "I'm hoping that a lot of the work I did this offseason is translating. I feel like I'm in a better tempo and a better position mechanically. I would've liked to have put a little finer point on that inning, but for my first outing, I'm really excited about it."

It would be hard to blame Doolittle for the self-criticism. The Nationals have eased him back this spring after he missed two weeks last August with right knee tendinitis and experiencing an extensive workload.

The 33-year-old southpaw threw 70 1/3 innings and appeared in 72 games between the 2019 regular season and postseason, his highest totals since '13 with the A's (73 1/3 innings and 74 outings).

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Due to the World Series run, Doolittle's offseason was a month behind its usual schedule, starting three weeks into November. He kept in regular contact with strength and conditioning coach Matt Eiden and athletic trainer Greg Barajas when he grew nervous about his readiness for camp, even cross-referencing with teammates regarding their progress.

Doolittle's daily maintenance program that began in August, when he spent time on the injured list, became the bedrock for his offseason routine. Five times a week, he used a stimulation machine that activates muscles.

Heavy lifting and dead lifts continued, but the emphasis was on the stability of his knee and getting it to work in conjunction with the hip better.

"It's allowed me to repeat things a lot better, get over my front side with better extension," said Doolittle, who compiled a 2.25 ERA in nine September appearances and a 1.74 postseason ERA upon his return. "A lot of things I was able to do in the playoff run I wasn't able to do in June and July. I really feel like I've turned a corner this last week or so in camp and I've picked up where I ended up in October."

That also happens to overlap with Doolittle trying out different grips on his secondary pitches. The club's starting staff has been watching his bullpen sessions and given him food for thought concerning his usage.

Doolittle acknowledged having trouble making the jump from throwing the pitches while warming up to committing to them in a game. Spring Training, it turns out, is a great chance to test them out in a less pressure-filled environment.

By his own count, Doolittle threw five sliders on Sunday and no changeups, since he faced only lefty batters. According to Statcast, he turned to his slider 5.8 percent of the time in 2019, compared to his 88.2 percent four-seam fastball rate.

"He's at a point in his career he wants to utilize two, maybe three pitches," manager Dave Martinez said. "He understands that, but my biggest thing with him is [the] elevated fastball. He's got to have command of that and get it up there. When he does that, he's really good."