Cardinals manager Mike Matheny told Martinez about the choice hours before his new ace allowed three hits in five scoreless innings in a 6-1 victory over Washington on Wednesday.
"I felt honored and, honestly, when he had this conversation with me I couldn't believe it," Martinez said through a translator. "I thought he was talking about the exhibition games in Springfield or Memphis. Just to be able to have this position and to be able to represent the Cardinals and be No. 1 and be the ace is so important to me."
Adam Wainwright had started the past four openers for the Cardinals. Matheny said Wainwright, who will pitch the second game, took the news well.
"It's nice having the conversation with somebody that just gets it," Matheny said.
The 25-year-old Martinez was an All-Star in 2015 and went 16-9 with a 3.04 ERA last year.
"There's going to be a lot of excitement that night," Matheny said. "That's going to be a fun game. Our stadium is going to be alive. It always is on opening day, anyhow. There's added stuff."
Wainwright was 13-9 with a 4.62 ERA last year. The pitchers talked after learning their spots in the rotation.
"We had a really good conversation," Martinez said. "The first thing that came out of his mouth was congratulations, and he just really advised me to take full advantage of this opportunity."
Matheny wouldn't commit to the remainder of the rotation. Lance Lynn will start against Triple-A affiliate Memphis in Tennessee on March 30, and Mike Leake will open the following day against Double-A Springfield in Missouri.
Matheny said Wainwright drew on experience gained as a minor leaguer in the Atlanta system, relaying a story about manager Bobby Cox determining whether to start Greg Maddux, Tom Glavine or John Smoltz on opening day by selecting the pitcher who finished highest in the previous year's Cy Young Award balloting.
"We talk so much about the healthy competition," Matheny said. "That's just another addition to that."
Martinez's start was his first since returning to the Cardinals from pitching with the Dominican Republic in the World Baseball Classic. Martinez had a 1.13 ERA in two WBC starts.
"An amazing experience, but it also helped me just recover from the offseason and just get back in that mentality -- and now even more that I'm going to be the opening day starter," Martinez said. "Having that adrenaline, having to be able to make the right pitches at the necessary time really helped me to now get ready for the season."