Leake hopes to lead the Reds to their seventh straight win at Citi Field while Mejia seeks to help the Mets avoid their worst home start in 22 years Friday night.
Following mediocre results over his first three years in Cincinnati (1-2), Leake (14-7, 3.37 ERA) finally came of age with career-best marks in wins, ERA, strikeouts (122), innings pitched (192 1-3) and starts (31) last season. He also looked strong in his last preseason tuneup Saturday, allowing two hits over six scoreless innings against Triple-A Louisville.
The right-hander had gone 2-1 with a 1.31 ERA in his previous five starts against the Mets (0-3) before surrendering four runs and eight hits in 1 2-3 innings of a 4-2 home loss Sept. 24 - his last start of 2013.
Now he'll face a New York team that totaled 10 runs and struck out 39 times while hitting .179 in losing all three games to visiting Washington in its opening series.
The Mets also have hit just .178 and scored 12 runs during their six-game home skid to the Reds, who took four of six overall in the series last season. Leake limited New York to three hits over seven innings in a 4-0 victory at Citi Field on May 21.
David Wright and Daniel Murphy are a combined 6 for 30 against Leake, though Lucas Duda has four hits in six at-bats in the matchup. Duda, however, has gone hitless in his first six at-bats in 2014.
"They only have a couple of guys that are still there. It's fairly a new team," Leake told the league's official website. "It's going to be a learning process the first inning or two because I won't know all of them."
Following a 3-hour, 42-minute rain delay Thursday, Cincinnati couldn't hold on to an early three-run lead despite Todd Frazier's two home runs in a 7-6 loss to St. Louis. Frazier, Joey Votto and Jay Bruce combined to go 7 for 13 with three homers and six RBIs after the Reds had totaled one run and nine hits in their first two games.
Votto has batted .464 over an eight-game hitting streak at Citi Field, while Brandon Phillips is hitting .346 over a 26-game run in New York that dates to the start of his career in 2006.
The Mets also hope to recover from their slow start after falling to 0-3 for the first time since 2005 in Thursday's 8-2 loss to Washington. They'll try to avoid dropping their first four at home since 1992 by giving the ball to Mejia (1-2, 2.30), who won a spot in the rotation after posting a 2.70 ERA with 13 strikeouts over 13 1-3 innings in spring training.
New York may need him to go deep into the contest since its bullpen has a 10.61 ERA, allowing 15 hits and seven walks in 9 1-3 innings along with a .366 opponents' batting average in 41 at-bats.
''I assure you, we're better than what you've seen the last three days,'' manager Terry Collins said.
Collins will be without Chris Young, who was placed on the disabled list with a right quad strain Thursday. Fellow outfielder Juan Lagares has played well early on, going 5 for 11 with four extra-base hits.
Wright, off to a 4 for 11 start this season, is 3 for 27 in his last eight games against the Reds.