Jay, 33, made quite a leap in the standings in going from a last-place team to the division-leading D-backs.
"I'm here just to help out in any way I can," Jay said. "I've been part of teams like this before. That's what's so exciting for me, to be back in this environment and get to the playoffs. That's a big goal, to get to October, and I'm looking forward to that."
Jay's postseason pedigree was one of the things that made him so attractive to the D-backs. He appeared in the World Series with the Cardinals twice, winning the championship in 2011. He's also been to the National League Championship Series five times.
The D-backs were in need of outfield help with center fielder A.J. Pollock and right fielder Steven Souza Jr. on the disabled list.
"He's a guy that's going to step in and fill a lot of roles here right away," said D-backs infielder Daniel Descalso a teammate of Jay's in St. Louis. "He can play all three outfield spots and give good at-bats, hit leadoff, brings that winning experience. He's been in a lot of playoff games, good teams. Just adding another good piece to our clubhouse."
Jay was in the lineup in right field and in the leadoff spot for the D-backs on Friday, and manager Torey Lovullo said Jay would start all three games against the Rockies.
Lovullo plans to use Jay in left and right field primarily, though he can also play center. Jarrod Dyson and Chris Owings figure to get most of the reps in center for now.
Jay has shown an ability to get on base -- compiling a .356 career on-base percentage -- and is known to be a thorn in the side of pitchers with the way he's able to work deep counts.
"That's my goal every day," Jay said. "I don't measure my success on results or anything like that. It's my quality of at-bats. If I'm seeing pitches, making the pitcher work, that's how I look at my at-bats. If I'm working them and if I can get to a 3-2 count and ground out, I'm happy that I worked the pitcher and I'll try to get them next time."
Injury updates Souza, who has a strained right pec, will take live batting practice Saturday against D-backs lefty Robbie Ray, who is on the DL with a right oblique strain.