Cousins' eighth-inning single tied Game 1 on Wednesday night and, in the second game of what has been a spectacularly competitive series, he again got the best of 51s' relief pitch Rob Carson.
With the bases loaded, Cousins worked the count to 3-2 by not biting on a couple of breaking balls by Carson that just missed the outside corner.
On a 3-2 pitch, Cousins lofted a high fly to short center field. With Marte tagging at third, Las Vegas' Brian Bixler made the catch. His throw to the place was a fraction of a second late and Marte was called safe by plate umpire Scott Mahoney.
"I can't remember how many pitches it was," Cousins said. "I just know the dude throws hard. ... I was just trying to put the bat on the ball against that guy. He's got a good off-speed pitch and I was able to lay off and got a fastball up in the zone that I needed to hit the fly ball."
Cousins wasn't surprised manager Keith Johnson, who was coaching at third, sent Marte on the short fly ball.
"Not at all," he said. "There's one out in the bottom of the ninth. I don't care who you are. You've got to try and win the game."
The victory means Salt Lake needs only one more win to advance to the PCL championship series against Oklahoma City or Omaha.
"That's huge," Cousins said. "That gives us a little cushion. We have to go down there and win one out of three instead of two out of three or three out of three. That's a huge difference, to win these two games at home."
Salt Lake took a 4-3 lead into the top of the ninth inning but, with two out, pinch-hitter Francisco Pena doubled in Jamie Hoffman with the tying run. Hoffman had singled off Bees' reliever Daniel Stange to keep the 51s alive.
In the end, however, Pena's clutch double to left center field simply set the stage for Salt Lake.
Marte opened the bottom of the ninth with a single.
He went to second on a passed ball by Pena. After Efren Navarro was walked intentionally, Drew Heid bunted to runners to second and third.
The 51s also intentionally walked Roberto Lopez to load the bases, sending Cousins to the plate for what would be his game-winning sacrifce fly.
Bees 5, 51s 4
R Scott Cousins' sacrifice fly scores Andy Marte in the bottom of the ninth inning, propelling the Bees to a 2-0 lead in the best-of-5 Pacific Coast League playoff series.
• Andy Marte's winning run caps a solid performance (4-for-5 with a home run and two runs).