PORT ST. LUCIE — Steven Matz is still making a pitch for the Mets’ Opening Day roster.

The lefty made 55 throws on flat ground Monday, a day after he was scratched from a scheduled minor league exhibition start with elbow tenderness, and indicated he hasn’t lost hope he can begin the season with the Mets.

But a club source indicated Matz will have to pitch in an exhibition game this week to be considered for that first start. With a new 10-day disabled list in play this season, the Mets could backdate a potential DL stint and still have Matz for the sixth game.

Zack Wheeler and Seth Lugo are contenders for Matz’s spot in the rotation if he is not ready to begin the season. According to pitching coach Dan Warthen, the lefty has been getting “long” in his arm swing and the two are working on finding a more natural arm slot.

Additional reporting by Joel Sherman