CHICAGO -- Chicago Cubs starter Jake Arrieta didn't necessarily circle his calendar when the schedule came out, but it's safe to say he's pretty excited to face his former team, the Baltimore Orioles, on Friday for the first time since being traded to Chicago last season.

"I've thought about it quite a bit," Arrieta said earlier this week. "I'm approaching it the same way as other games."

There's a quiet confidence to Arrieta these days that wasn't around when he was traded to the Cubs in July 2013 along with pitcher Pedro Strop for starter Scott Feldman and catcher Steve Clevenger. Feldman was 5-6 with a 4.27 ERA in 15 starts for the Orioles, who missed the playoffs, but he departed via free agency. The Cubs were left with a blossoming 28-year-old pitcher whose head has seemingly caught up to his arm.

"It's no surprise," Orioles manager Buck Showalter said of Arrieta this week. "Wish him well. I like Jake. It was a good move for both of us."

That's underselling how Arrieta has developed since struggling after being the Orioles' Opening Day starter in 2012. His ERA that season was 6.20 in 24 games, including 18 starts. At the time of his trade to the Cubs, Arrieta sported a 7.23 ERA and a 1.77 WHIP in five starts.

Heading into Friday's start, Arrieta ranks seventh in the National League among regular starters with a 2.61 ERA in 19 starts and has taken over as the Cubs' ace since they traded Jeff Samardzija to the Oakland Athletics in July.

"I don't think it surprises anybody that Jake and Petey [Strop] have done well, but timing's everything," Showalter said. "I think it was a good move for their career, both of them, and I'm excited that it's worked out for them. I hope it doesn't work out Friday."

More times than not, it has worked out for Arrieta, who has flirted with no-hitters and perfect games this season by using devastating off-speed pitches.

But that wasn't always the case. He couldn't command his stuff in Baltimore, leading to a career-high five walks per nine innings pitched last season. The further he gets from the trade the less Arrieta likes to talk about his struggles in Baltimore where he and former pitching coach Rick Adair didn't see eye-to-eye. It wasn't a hostile relationship, but it didn't bring out the best in Arrieta on the mound.

"There were some things there that inhibited my ability to take that next step," Arrieta said last year. "There were things going on there that kind of restricted me a little bit."

Which means the change of scenery may have been the best thing for him.

"I think it was a factor that helped," Arrieta said. "It was kind of that time."

After struggling in five starts with the Orioles before the trade last season, Arrieta paid immediate dividends for the Cubs, posting a 3.66 ERA and 1.12 WHIP in nine starts. He showed enough to convince the Cubs that he belonged in the 2014 rotation.

After overcoming shoulder stiffness that limited him in spring training and kept him out of the rotation until early May, Arrieta has taken off, becoming one of the most dependable starters in the National League. The difference, according to his catcher, is confidence.

"It's a big difference from last year to this year," Welington Castillo said. "The more important thing he has this year is his confidence. He throws any pitch in any count no matter who's the hitter.

"If he knows there's one pitch is not where he wants it, right away he knows what he's doing bad. He knows what to do mechanically and physically to put the pitch where it needs to be."

Arrieta, who has allowed three earned runs or fewer in 13 of his past 14 starts, says he gets most "amped" about two hours before a start. By the time he takes the mound Friday against some good friends, he thinks he'll have calmed down enough to pitch like he's capable.

"They have a great team," he said. "A really good team. If I execute, I'll be OK. If I don't, I'll get into trouble."

Is there anything to prove to the team that sent him packing?

"I don't look at it that way," Arrieta said. "I like how far I've come. It's happened to a lot of players. They hit the ground running and they take off. I was a candidate for it."

ESPNChicago.com's Doug Padilla and Sahadev Sharma contributed to this report.