PHILADELPHIA -- It is too early to worry, even for jumpy Phillies fans, but it is not too early to wonder.

Is anything up with Seranthony Domínguez and the Phillies’ bullpen? Dominguez walked a batter, hit a batter and allowed a three-run home run on a 95.3 mph fastball to Eddie Rosario in the top of the ninth inning Saturday in a 6-2 loss to the Twins at Citizens Bank Park. Dominguez has allowed runs in two of three appearances this season and his fastball velocity is down from 97.9 mph last season to 96.7 mph on Saturday, according to Statcast.

“I’m not worried at all,” Dominguez said through the team’s interpreter. “I think that the more I pitch, my velocity is going to get better. I feel 100 percent.”

Dominguez is part of the team’s 1-2 punch in the back of the bullpen with David Robertson. Robertson allowed runs in each of his first three appearances before pitching a scoreless ninth inning Friday. Robertson said the coaching staff discovered a simple mechanical flaw in his delivery. He made the adjustment Friday and he believes he should be fine moving forward.

“It was terrible,” Robertson said. “To be able to get out there and be able to show these guys what I'm capable of doing is nice. I feel like it's tough when you take three bad outings in a row and you've got to put it behind you because it's the life of a reliever. To get one good one under my belt helps.”

Dominguez and Robertson have a combined 15.19 ERA, allowing nine hits and eight runs in 5 1/3 innings. They have walked seven and struck out seven.

Everybody knows they need to be better. The expectation is they will be better. But their early struggles also highlight the importance of their successes if the Phillies want to make the postseason. The Phils are not going to score runs in bunches every night. In fact, Saturday was the first time this season they were unable to score at least five. There will be many nights when they will need their best relievers to put up zeros to hold a narrow lead or maintain a small deficit.

“You want everything to be smooth from the start,” Phillies manager Gabe Kapler said. “It hasn't been from a bullpen perspective. But there have been some bright spots. Ultimately we've had opportunities to close the door on their offense a couple of times and we haven't been able to do it. We have to go back to the drawing board and get together… and just get a game plan together to fix it.”

Dominguez offered no explanation why he feels he needs more time to get his fastball velocity up, although some hard-throwing pitchers continue to build arm strength early in the season. Dominguez’s fastball averaged 97.5 mph last May, when he first joined the Phillies.

“It's something that we've been working on with him, really using his legs and driving off the slope,” Kapler said.

Bryce continues to impress

Bryce Harper turned a single into a surprising double when he hit a ball to right-center field in the sixth. Harper never stopped running, and by the time Twins center fielder Byron Buxton fielded the ball, Harper had reached second base.

Buxton later threw out Harper at the plate when Cesar Hernandez hit a fly ball to center. Harper tried to leap over Twins catcher Willians Astudillo to avoid the tag, but could not.

“You have to take a chance,” Kapler said. “You have to make the outfielder throw you out. It's going to take a perfect exchange and throw in that situation. Given the situation of the game, I thought it was the right call by Dusty [Wathan], the right call by Bryce.”

Arrieta economical in loss

Jake Arrieta allowed five hits, three runs and three walks in seven innings. He struck out one, but allowed back-to-back home runs to Max Kepler and Astudillo in the third. He threw just 75 pitches.

“Another day with a lead, I could've probably thrown a [complete game] today without a problem,” Arrieta said.

Arrieta mustered just one swing and miss, which tied for the lowest swing and miss rate (1.3 percent) in a start in his career.

“Going into this game, I knew these guys were going to be aggressive in the strike zone and even out of the strike zone,” Arrieta said. “I had a lot of guys 0-2. I just threw some hittable pitches which went for some base hits. Just need to clean that up, need to be a little bit better outside the strike zone when I get ahead of those guys. Not really concerning. Moving forward, just need to clean up the tightness of my secondary stuff to put some of those guys away when I do have them in two-strike counts.”