Willie Mays came up to the Giants on May 25, 1951. He led the team to the National League pennant that year.
Buster Posey came up the the Giants (after a sip of coffee in 2009) on May 29, 2010. He led the team to the National League pennant this year.
In 1951, Mays had 464 at-bats. Posey had 443 this year.
Mays had 127 hits. Posey had 124.
Homers? Mays 20, Posey 18.
On-base percentage. Posey skunked him: .357 to .356.
Rookie Mays hit 22 doubles. Rookie Posey hit 23.
That year, Mays struck out 60 times. This season, Posey struck out 55 times.
Runs and RBI? Mays 59 and 68. Posey 58 and 67.