PHILADELPHIA -- Jake Arrieta describes the bone spur in his right elbow as a “pretty good marble” that blocks the joint.

It causes pain every time he pitches, but he said he will try to pitch with that pain the remainder of the season, hoping he performs well enough to stabilize a rotation that ranks toward the bottom in the National League.

Arrieta’s efforts Sunday afternoon at Citizens Bank Park -- he allowed four hits and one run in five innings -- set up Maikel Franco’s walk-off home run to left-center field with two outs in the ninth inning in a 4-3 victory over the Nationals. Franco’s 100th career homer prevented a series sweep and moved the Phillies back into the second NL Wild Card spot.

“We needed this game so bad,” Franco said.

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But Arrieta’s presence and performance in the rotation moving forward is worth watching closely. The rotation entered Sunday ranked 11th in the National League with a 4.53 ERA and last with a 5.02 FIP.

Phillies ace Aaron Nola has a 0.76 ERA (three earned runs in 35 2/3 innings) in five starts since June 15, while the rest of the rotation has a 6.62 ERA (66 earned runs in 89 2/3 innings) in 18 starts.

“The more pitches I throw, the more difficult it becomes,” Arrieta said. “It doesn’t feel good, I’ll tell you that.”

“What did 85 percent of Jake look like for us? That's it, right?” Phillies manager Gabe Kapler said. “It's a guy who can fight through some discomfort. It's a guy who can fight through not being at his best but can still give us a chance to win. Really impressive, gusty, resilient effort by Jake.”

Arrieta’s fastball velocity averaged 93.2 mph through two innings, but 91.3 mph in the third, 92.9 in the fourth and 91.0 in the fifth. He threw his cutter just once in his last two starts. He threw the pitch 15.2 percent of the time in his first 17, according to Statcast.

“That’s probably the pitch that has hurt the most and it has been most affected by this bone spur,” Arrieta said. “I’m attempting to throw that pitch the same as I always have, but I’m just not able to get it to do what I usually am able to get it to do. The break isn’t there. I’ll use it certain times, but any time I have to turn my hand sideways on the curveball or the cutter, it gives me some issues.”

It leaves Arrieta with a sinker, curveball and changeup. He said it can be enough.

“My curveball and changeup combination for me are usually really good and if I can locate that and get ahead of guys and use those pitches in situations to get them to put the ball on the ground and get swings and misses, I’ll do that,” Arrieta said.

Of course, it would be a mistake for the Phillies to bank on Arrieta pitching like this the remainder of the season. At some point the pain might become intolerable. Nobody knows. What they really need are right-handers Zach Eflin, Vince Velasquez and Nick Pivetta to pitch better. The trio faces the Dodgers in that order in the first three games of a four-game series, beginning Monday night.

“Obviously we need them to step up and be a little bit better for us and I think they will,” Arrieta said. “They know what’s at stake. They’re well aware of that. We believe in the group we have, regardless of what I’m going through. I still know what I’m capable of even with this issue. We need some more out of our starters collectively and I think that’s been the message from Day 1.”

The Phillies could look for help from outside. Two postseason contenders just found reinforcements for their rotations at little cost. The Red Sox acquired right-hander Andrew Cashner (9-3, 3.83 ERA, 4.25 FIP) from the Orioles for two 17-year-old prospects and cash. Neither prospect ranked among Boston’s top 30. They are essentially lottery tickets. The Red Sox will pay Cashner less than $2 million. The A’s acquired right-hander Homer Bailey (7-6, 4.80 ERA, 4.47 FIP) for a Double-A infielder Kevin Merrell, who was their No. 17 prospect. Oakland will pay Bailey about $250,000.

The Braves signed free-agent left-hander Dallas Keuchel (3-2, 3.09 ERA, 4.89 FIP) last month. The Phillies had no interest in him.

It is difficult to imagine the Phillies acquiring a pitcher like Giants left-hander Madison Bumgarner. He will cost a lot and Phillies president Andy MacPhail said Friday the team is more than one player away from winning a World Series, indicating they are unlikely to trade top prospects for a rental.

“I think the group in here can do it,” Arrieta said. “We just need more productivity out of some of our guys. It’s plain and simple. It’s easy to always look outside for the solution. It might be cliché, but we have the guys here that can continue to win on a consistent basis, we just need to perform and that’s really all there is to it.”