For important dates in San Francisco Giants history, it might be appropriate to add May 29, 2010. It was on that day the team recalled Buster Posey, the baby-faced 23-year-old catcher, from Triple-A Fresno.

It is difficult to recall a more transformative moment for the franchise, but already people are taking stabs at it. On Monday, Scott Ostler, in the Chronicle (link available Wednesday under the Chron’s strategic embargo policy), drew comparisons with the call-up of Willie Mays in 1951. Resident Merc skeptic Tim Kawakami called Posey “easily the Giants’ best position player since Barry Bonds’ last great fully healthy year, which was 2004.”

Baseball, more than most sports, is a game of individuals, but the change with Posey in the lineup is remarkable. The Giants, through May and much of June a hapless and largely preposterous team, are reborn. As Posey extended his hitting streak to 20 games Tuesday night in a 6-4 win over the Marlins, the full measure of his impact was coming into view. His presence is having a "profound psychological effect on the entire Giants lineup," which outlasted the league ERA leader, Josh Johnson, before pounding out the win. 

Posey's hitting streak ties the longest in the majors this season and is the second-longest by a Giant rookie since Willie McCovey hit in 22 straight games in 1959. He is hitting .449 in July, with 40 hits. The Giants are leading the Wild Card race and last night moved 2 1/2 games behind the Padres, the closest they've been in over a month.