"Of course I think we're a playoff team," Arrieta said Monday after the Phillies completed spring training with a 3-2 win over the Tampa Bay Rays.
The 33-year-old right-hander allowed two runs on six hits and struck out eight over six innings. He induced 20 swings and misses.
"Lots of empty swings," Phillies manager Gabe Kapler said. "That was the most encouraging thing about the day. Super encouraging. Strong in his legs. Delivery was easy. Arm slot was perfect. I thought everything looked really good."
Philadelphia opens at home Thursday against NL East champion Atlanta. The Phillies transformed during the offseason, signing right fielder Bryce Harper to a $330 million, 13-year contract after adding left fielder Andrew McCutchen, shortstop Jean Segura and catcher J.T. Realmuto.
"It's exciting," Arrieta said. "With the guys we've got, there's not really a break in our lineup. It's going to be a fun one."
Arrieta was a key contributor to the 2016 Chicago Cubs, who won the team's first World Series title in 108 years. He went 2-0 in the seven-game Series against Cleveland.
Philadelphia, which led its division with the second-best record in the NL one week into August, lost 33 of its final 49 games.
"A lot of guys in here remember the way it shook down for us, the way the season finished, and we don't want that to happen again," Arrieta said.
Philadelphia went 80-82 in its sixth consecutive losing season.
"I think this team has a ton of potential," Kapler said. "But we've got to stay focused every single day. Got to come to the ballpark with a game plan of doing the little things right. Running the bases hard and executing the fundamentals. If we do those things, I think we can do good things."
Harper doubled to left-center on a 95 mph fastball from Wilmer Font in the first and walked against Diego Castillo during the third. After starting 0-for-9, the slugger closed out spring training with four hits -- including a double and two homers -- in his final eight at-bats.
"I think Harper caught up pretty quick," Arrieta said. "He's one of the brightest stars in our game. If he stays healthy and is on the field for us, he's going to put up some great numbers."
In his final plate appearance, Tampa Bay used a defensive alignment shifted toward the opposite field that left a large hole between first and second base.