Prior to Castellanos scoring, all six of the earned runs Chen allowed over his five Grapefruit League starts came on solo homers. Chen also surrendered an unearned run in his previous outing.
"There's still some little things I need to work on more, but overall I think I'm ready for the season," Chen said via an interpreter.
Chen surrendered only that one run in three innings of work on Saturday. It could have been much worse.
Detroit loaded the bases with no one out on a double and two walks in the second inning. The next batter, Andrew Romine, smashed a line drive down the first-base line that Justin Bour snared, then stepped on first to double off Alex Avila. Ian Kinsler grounded out to second to end the inning.
"In the past when I fell behind I tried to be too eager to get back into the count, so I may throw a strike down the middle," Chen said. "Now I'm trying to have the mindset not to be afraid of walking a guy."
Chen concluded spring winless in six appearances.
"This year we had a longer Spring Training than usual so you had time to work things out at my pace and work on my offspeed pitches," Chen said. "I feel my offspeed pitches are a little better than last year. Now I think I'm pretty much ready for the season. I'm excited to go."
Chen allowed a hit to begin the third inning but faced the minimum in his final frame after inducing an around-the-horn double play off the bat of left fielder Ross Kivett. Tom Koehler followed Chen on Saturday and improved to 2-2 on the spring by allowing one run on four hits in three innings.
The righty will be the No. 3 starter in the Marlins' rotation. Chen will get start No. 4 when the Marlins travel to face the New York Mets on Friday.
Chuck King is a contributor to MLB.com and covered the Marlins on Saturday. This story was not subject to the approval of Major League Baseball or its clubs.