Mike Olt hit a pair of homers and the Cubs scored four runs in the sixth inning thanks to three Mariners errors to take a three-run lead into the late innings. But a two-run single by James Jones and an RBI single by veteran catcher John Buck in the ninth sent the game into extras.
Robinson Cano, signed to a 10-year, $240 million deal this winter, continued his hot spring for the Mariners, hitting a pair of doubles to run his average up to .632 (12-for-19) in Cactus League play.
Olt homered off Mariners starter Randy Wolf in the second and shortstop prospect Javier Baez hit a towering shot off Wolf in the fourth inning. Olt, a candidate at third base limited to playing first base and designated hitter in recent days with some tenderness in his right shoulder, blasted his second homer of the night and third of the spring off lefty Charlie Furbush to start the four-run sixth.
After that, the Mariners committed three errors and John Baker delivered a bases-clearing double to break the game open. Olt added an RBI single in the seventh to match Baker with a three-RBI night.
Cubs starter James McDonald, coming off a rough 2013 campaign and vying for a spot in the rotation, allowed two earned runs on two hits and five walks over 2 2/3 innings in his second Cactus League start.
Cano gave the Mariners the first lead with an RBI double to score Kyle Seager in the first, and Brad Miller gave Seattle a 3-2 lead with a solo homer to right-center, his third of the spring.
McDonald threw 64 pitches, 26 for strikes, but he was happy with how he escaped jams. He's working on his two-seam fastball in hopes of getting more ground-ball outs.
"All in all, I'll take away from this is that's how you compete, that's how you go after guys," McDonald said. "You keep going, keep going. It's not always going to be 1-2-3, 1-2-3."
Wolf, a veteran non-roster invitee for the Mariners, was charged with two runs on the two homers while allowing six hits in four innings, striking out three without walking a batter.
"Obviously, you don't want to give up hits or give up homers, but to me there was a lot of progress, a lot more positives than negatives today," said Wolf, who missed all of 2013 after having Tommy John surgery. "I threw a lot of strikes and got ahead of a lot of guys."
Cubs manager Rick Renteria challenged a bang-bang out call at first base in the fourth inning, but the call was upheld after a review of instant replay.
Up next: After an off-day Thursday, the Cubs return to action on Friday, playing host to the Dodgers at Cubs Park. Kyle Hendricks, the Cubs' 2013 Minor League Pitcher of the Year, gets the start. This will be Hendricks' third Cactus League start. In his last outing against the Brewers, he gave up two runs on three hits over three innings. First pitch is scheduled for 3:05 p.m. CT, and there will be an audio broadcast of the game exclusively on Cubs.com.
John Schlegel is a national reporter for MLB.com. You can follow him on Twitter at @JohnSchlegelMLB.