WASHINGTON -- No pitcher in baseball has been standing on the mound at the end of the game more frequently than Nationals closer Sean Doolittle. He barely held onto a three-run lead in the ninth inning on Monday night, yielding a pair of runs to the Reds before shutting the door on the Nationals’ 7-6 victory at Nationals Park, the Major League leading 48th game Doolittle has finished this season.

With each passing appearance, however, Doolittle is starting to creep into territory he has not navigated in years, thanks to injuries that had derailed so many of his previous seasons. Doolittle has already made 52 appearances this season, nine more than he made in 2018 and just one off his total in ’17, when he first joined the Nationals midway through the season. He is on pace to pitch more frequently than he has in any season since 2014 (61 appearances).

• Box score

And what might be worrisome for Washington is that these outings are not going as smoothly for the once automatic Doolittle, who hinted that he was feeling fatigued after Monday’s game.

“I mean, that's 5 of 7, in the middle of August in the first season where I'm still going,” Doolittle said with a laugh. “I haven't put together a season like this in awhile. I'm starting to feel it a little bit. These are the nights where you've got to dig deep and grind it out.”

During this stretch of five out of seven games, Doolittle has surrendered 10 hits with a walk and three strikeouts while giving up six runs in 4 2/3 innings (11.57 ERA), most of which came during a blown save in New York on Friday. And Monday’s game continued some of those troubling trends for Doolittle, who has looked oddly hittable lately.

He has given up 56 hits, already a career-high, in 50 2/3 innings, and he holds a 1.34 WHIP, which would also mark a career high. He is not missing bats as frequently as he once did, with a swinging strike rate that has dipped to 12.5 percent this season, and opponents are batting .271 against him.

Even with an overhauled bullpen, the Nationals have so few reliable relievers and have been involved in so many tight games that they have needed to lean on their closer heavily. Doolittle has been open to talking about his heavy workload, but he has also acknowledged that he has to find ways to deal with it.

“It's mid-August, everybody's gassed,” Doolittle said. “It's a marathon, for sure. The good teams find a way. The good players find a way to catch that second wind.”

What gives manager Dave Martinez confidence is that Doolittle’s fastball velocity has not dipped and that on most nights, despite how dicey things might get, he is still able to get the job done in the ninth.

On Monday, the Reds collected three hits in the ninth, starting with a pinch-hit home run from Phillip Ervin, the seventh homer Doolittle has surrendered this year, also a new career high. Jose Iglesias singled and Joey Votto won a nine-pitch battle, driving in another run to cut the Nats’ lead to one. Following an intentional walk, Doolittle was able to rebound and induce a popout from Josh VanMeter to seal the win.

“I really think he’s throwing the ball well,” Martinez insisted. “Look, he’s facing Votto, he faced that Irving kid, Iglesias is no easy out. But he got the outs that we needed and he was there to save the game.”

So Doolittle has been trying to find ways to stay fresh while still pitching so frequently. He has altered his routine a bit before games, playing catch more efficiently and throwing off the mound less frequently to preserve his arm. He made some changes to his workout routine in between and after outings.

The Nationals’ bullpen has been troublesome all season, entering Monday with the worst ERA in baseball of any team but the hapless Orioles. But the one constant has been Doolittle, and they cannot afford to have him at anything less than full strength.

“You really want to be playing your best baseball in September and peaking at the right time. There's still every opportunity to do that,” Doolittle said. “I've hit a couple of speed bumps here, recently. It hasn't been as smooth as I wanted it to be, but I can still accomplish everything. The team can still accomplish everything we set out to at the beginning of the season.”