Mets manager Terry Collins informed Gee of the decision Monday.
''It's a big honor,'' Gee said. ''I'm very thankful for that opportunity, but really I've just got to take it like any other game. It's just one of 30-something starts I hope to get this year, but it's definitely a big honor.''
Gee went 12-11 with a 3.62 ERA in 32 starts last year, when he had a 6.34 ERA after eight weeks and almost lost his spot in the rotation. He had a 2.71 ERA during the final four months.
Gee is 1-0 with 1.69 ERA in three exhibition starts with eight strikeouts and no walks.
''I don't think about where I've come from in the last year,'' Gee said. ''I'm just going to keep going forward. That's where I'm at.''
Jonathon Niese was expected to be the Mets' opening-day starter for the second straight year, but he has been sidelined by shoulder and elbow injuries. Niese threw off a mound Monday for the first time since receiving a cortisone shot on March 17 and is hoping to be ready by April 6.
''It's kind of by default, too,'' Gee conceded. ''I mean Jon Niese has a few setbacks, he can't make opening day, so I get it. It's a big honor. I've definitely worked my way up. I just try to work hard and go out there and try to win games. To be out there on March 31 will be pretty cool.''
Daisuke Matsuzaka, a non-roster invitee trying to make the roster, allowed one run in six innings as the Mets beat the St. Louis Cardinals 5-3.
''Throughout spring training, condition-wise I felt great, but the results weren't exactly what I was hoping them to be,'' Matsuzaka said through an interpreter. ''Today I went up there knowing this would be my last chance to show what I can do up there.''
Matsuzaka, who is competing with Jenrry Mejia to be the Mets' fifth starter, allowed three hits runs, walked three and struck out five. He hit Stephen Piscotty on the back of the helmet with a changeup opening the seventh inning and was replaced by Vic Black.
Daniel Murphy went 2 for 3, including a two-run double off Shelby Miller in the third inning.
Miller gave up three runs and three hits in five innings. He struck out four and walked three.
''I thought it went all right,'' Miller said. ''Obviously, I still have some stuff I need to work on still. I kind of struggled a little bit in the third with my command, but other than that I'm getting back to where I want to be. I feel like I'm putting it all together.''
CLOSE CALLS FOR PISCOTTY
In addition to being plunked on the head, Piscotty collided with center fielder Peter Bourjos on a fly ball by Travis d'Arnaud to right-center in the second inning. Bourjos made the catch but stumbled over Piscotty, allowing Chris Young to tag up and advance to third.
''We had a little, I don't know if it was a miscommunication, but we got figured it out late,'' Piscotty said. ''I kind of hit the deck at the last second tried and get out of the way the best I could.''
The Mets released reliever Kyle Farnsworth on Sunday, but he remained with the club Monday and said he expects to be re-signed Tuesday. ... Collins said he is concerned about Black, who allowed two runs without recording an out. Black has a 6.75 ERA in nine appearances. ... Mets LHP John Lannan, working as a reliever, made back-to-back appearances for the first time in his pro career. He pitched one perfect inning and struck out Matt Carpenter.