PHOENIX -- Shelby Miller, who underwent Tommy John surgery last year, threw his sixth bullpen session Friday and is making progress toward a possible June return to action.
Miller threw 35 pitches at an estimated 80 percent effort.
"I was letting a couple go and kind of testing it a little bit to see how it feels," Miller said. "All my curveballs were really good. Cutter is decent right now. Fastball is amazing. Ball is coming out good."
The one pitch that Miller has yet to throw in his arsenal is the split-finger fastball because that is a pitch that tends to tax the arm more than others.
Miller is due for a five-day shutdown period coming up, then he will resume throwing bullpen sessions.
"Timing is good, arm feels good," Miller said. "I can't imagine having to wait too much longer before I get into live games."
Randall Delgado (left oblique) threw a 30-pitch bullpen session. The next step for the reliever will be a simulated game Tuesday.
Ride or jog?
The D-backs used five relievers on Opening Night, and none of them rode the team's new bullpen cart onto the field.
Setup man Archie Bradley declined to use it in the seventh because he wanted the feeling of a sellout crowd cheering for him when he ran out onto the field.

In the future, he might use the cart.
"I just kind of wanted to be in my normal routine at least for the first one," Bradley said. "Hopefully as the season goes, get the feet settled, the arm settled, the jitters settled a little and then start to take it, maybe. I think it's always going to be situationally based."
Closer Brad Boxberger, who did not pitch in the game, said he likely would not use the cart this year.
The right-hander, like many players, likes to stick to a very strict routine. With the D-backs being the only team in baseball to currently utilize a cart, it would mean he has a different process at home than on the road.
"I can see it catching on in the future when more stadiums have them, so you can stick to your routines," Boxberger said. "But for a guy who is routine-oriented, it's hard to make that change."