WASHINGTON -- Gabe Kapler traveled to Rhode Island in December for a meeting with David Robertson, hoping to get a better understanding of the pitcher the Phillies believed could bolster their bullpen.

Robertson, who allowed the winning run of Wednesday’s 9-8 loss to the Nationals, had spent the majority of his career as a Kapler-style reliever, pitching in various innings and various roles in various situations. Kapler, shortly before the Phillies signed Robertson to a two-year, $23 million deal, asked the reliever how he hoped the Phillies would use him.

“I was listening very carefully,” Kapler said earlier this week. “He said, ‘I just want the ball in the most important moment. I don’t really care when it is.’”

Robertson had the ball Wednesday in the most important moment at Nationals Park. For the third straight time, he faltered. Robertson loaded the bases in the ninth inning without an out. He then ended the game by issuing a walk-off walk to a player who was sent to triple A after the game. Jake Noll flipped his bat. Robertson ducked his head and walked off the mound.

The Phillies, after opening the season with four straight exhilarating wins, had tasted defeat for the first time. They picked a painful way for it to happen.

“I’ve been [stinking] out there, that’s for sure,” said Robertson, who has allowed runs in each of his three outings. “I throw it over the plate, it gets hit. Not throwing strikes, walking guys, putting guys on, giving them every chance to score runs. I’m pitching like crap.”

Robertson became the first Phillies pitcher since Juan Perez -- remember him? -- in 2011 to walk three batters without recording a single out. He began the season as one of Kapler’s most trusted relievers for his ability to handle both left-handed and right-handed batters. But all of his three outings have resulted in runs scored.

“He hasn’t been at his sharpest,” Kapler said. “He hasn’t had command of his cutter. He hasn’t been able to land his curveball when he wants to land his curveball, and those are his calling cards. He is a guy we will be leaning on heavily and depending on and very much betting on to perform well for us.”

This offseason, the Phillies chose to invest in their bullpen instead of adding to their starting rotation. They signed Robertson, picked up Juan Nicasio and Jose Alvarez in trades, and returned Seranthony Dominguez, Hector Neris, Edubray Ramos, Adam Morgan, Tommy Hunter, and Pat Neshek. The later innings, the Phillies made clear, were the priority. And no pieces were more essential than Robertson and Dominguez.

Dominguez, who was on the mound in the eighth inning when the Nationals tied the game, has yet to show the electricity he rode last season. Hunter is out with a sore arm and might not be available soon. Robertson, who said he’s “tired of doing bad out there,” has not been reliable. The bullpen, through the first week of the season, was not a perfect unit.

“I saw our bullpen as a strength coming into spring training, and I saw our bullpen as a strength when we left spring training, and I see our bullpen as a strength now,” Kapler said. “I just don’t think we’ve had our best games yet as a 'pen.”

The bullpen’s shortcomings spoiled what seemed to be another exhilarating win despite a poor start by Aaron Nola -- the ace allowed six runs, including two home runs, in just three innings.

The Phillies scored four times in the eighth inning to take an 8-6 lead. Andrew McCutchen drove a bases-loaded, three-run double to center field. Scott Kingery sprinted to score from first base. He dived into home and somehow contorted himself around the tag from catcher Yan Gomes. Jean Segura followed with an RBI single.

A season ago, that two-run lead would have felt like 20 runs, with Dominguez waiting in the bullpen. But the pitcher looked human on Wednesday. Gomes tagged him for an RBI double, putting Dominguez on the ropes. He seemed to battle back when Adam Eaton tapped a two-out grounder to the mound. Dominguez gloved it, hesitated slightly, and tossed it to Rhys Hoskins at first base. Hoskins reached out his mitt but snapped it shut before the ball reached him. The throw skipped past him, Gomes scored, and the game was tied.

“Have to catch it,” said Hoskins, who was charged with an error. “I missed it.”

An inning later, Robertson was walking off the mound as the Nationals celebrated an exhilarating win of their own. He did not break his stride as he walked to the dugout, ambled down the dugout steps, and moved to the clubhouse. It was a tough first week for a pitcher the Phillies hoped could bring such promise.

“It’s baseball,” Robertson said. “You’re not going to be good every time, it’s a game of failure. I don’t like going out there and failing every time. Just going to have to figure it out.”