In his most recent outing against Quad Cities on June 11, Rhee tossed four solid innings, holding the St. Louis Cardinals' affiliate to just one hit and an unearned run.
This season, Rhee has three victories and has held opposing hitters to a .189 average overall, and that has taken the Cubs' front office by surprise.
"We honestly thought he'd be a Boise candidate, but he's surpassed all of our expectations," said Cubs Vice President of Player Personnel Oneri Fleita. "Maybe it's because he doesn't understand enough to be nervous."
Fleita is referring to the fact that Rhee, who was signed by Cubs Pacific Rim Scouting Supervisor Steve Wilson in August of last year, is still learning the English language in his first year in the U.S. The Cubs don't have many people that speak affluent Korean, Fleita said, so it has been a learning experience for both sides.
"We're getting to know him and he's getting to know us," Fleita said of Rhee. "He's got us beat so far, but coming from Korea and impressing everyone like he did in Spring Training, he's got a nice mix."
Pitching with what Fleita called a "three-pitch mix" (fastball, curveball and changeup), Rhee has shown his maturity by being able to compete right away, Fleita said.
Mostly, he's done it just by throwing strikes. This season, Rhee has walked only eight batters and has struck out 21.
"He has shown us a lot of poise," said Fleita.
Morever, the Cubs do not appear worried over Rhee's health. During his stint on the disabled list, the club wasn't concerned enough to send Rhee to Extended Spring Training, instead letting him throw in simulated games with Peoria, Fleita said.