Right-hander Archie Bradley is still in the mix, and Lovullo said there are even more than that.
"A few guys may have solidified their spots more than others, but it's still open," Lovullo said. "It's all wide open. I'm not saying that there are just six guys who are competing. There are more than six guys competing every day. I don't want to put a tag on that yet, but they're all still competing."
Sliding into form: Walker gave up his first runs of the spring in Wednesday night's 7-3 win over the Cubs, but more importantly for him, his slider is becoming a weapon.
Walker, who struck out eight over four innings, has tried throwing a slider the past couple of springs, but it had more of a cut-fastball break to it. Now it's sharper like a typical slider.
"Now that I'm actually throwing it and having confidence in it, I know the break that I want and I know I can get the break if I just throw it," Walker said. "I think that's the biggest thing this year from the previous years is really having that confidence in throwing it."
Thole out: Catcher Josh Thole sustained a left hamstring injury in the eighth inning when he tried to avoid Ronnie Freeman's hit to right field.
Lovullo said postgame that Thole felt his hamstring "pop."
Steve Gilbert has covered the D-backs for MLB.com since 2001. Follow him on Twitter @SteveGilbertMLB. This story was not subject to the approval of Major League Baseball or its clubs.