Jason Bay hit a two-out, two-run homer in the bottom of the ninth off Mariano Rivera to tie a game that seemed lost, and two innings later, Kevin Youkilis launched a walkoff homer off Damaso Marte over the Monster seats, giving the Sox an improbable 5-4 victory over the Yankees in the first meeting of the year between the two rivals.

The Sox stranded 14 runners and were just 2-for-14 with runners in scoring position while hitting into four double plays.

But the blown save by Rivera was the 12th of his career in the regular season against the Red Sox , and six relievers followed starter Jon Lester and helped the Sox extend their winning streak to eight games.

Down to their final out, Bay's homer, his fourth of the year, was driven to center on a 1-and-0 pitch and scored Youkilis.

The late-game heroics helped make up for a meltdown in the seventh by the Sox bullpen. Coming into a 2-2 game, Hideki Okajima yielded an opposite-field double to Derek Jeter, a bunt single to Johnny Damon, a fisted single to center from Mark Teixeira and a blooper to right by Jorge Posada before being relieved by Manny Delcarmen.

Delcarmen retired all three hitters he faced, but Robinson Cano managed a sacrifice fly, scoring the second New York run of the inning.

The Sox later worked out of a bases-loaded jam in the top of the ninth when Javier Lopez walked two batters and hit another.

Earlier, Nick Green, a longshot to make the team until the Sox lost not one but two shortstops to injury, delivered a run-scoring single to score Mike Lowell and chase Joba Chamberlain in the bottom of the sixth inning. Green spent last season playing for the Yankees' Triple-A affiliate.

The Sox threatened further, but Yankees right-handed reliever Phil Coke, inheriting two baserunners, got Jacoby Ellsbury to fly to center and Dustin Pedroia to fly to right, preserving the 2-2 tie.

Lester kept the Sox in the game, allowing just two runs, but his high pitch count (115) limited his outing to just five innings.

Chamberlain, meanwhile, repeatedly got himself into trouble, but the Sox helped him out by hitting into four double plays in the first five innings.

The Yankees pushed a couple of runs across against Lester in the fourth. Melky Cabrera (single) and Jose Molina (walk) were on first and second when Cody Ransom pulled a ball just inside the third base bag which kicked off the grandstand into shallow left. Cabrera scored from second as Molina took third on Ransom's double. A groundout to short by Jeter then plated Molina.

Lester pitched out of some trouble in the second and third innings. He issued back-to-back, two-out walks to Cabrera and Molina before fanning Ransom.

- smcadam@bostonherald.com