DENVER -- Bob Melvin likes the talent of the relievers he has down in the bullpen, he is just not always crazy about the results they produce.

After being a strength of the team during its march to the National League West crown in 2007, the D-backs' bullpen has struggled at inopportune times in '08.

"I think this year to a man we've had some struggles with every one of those guys," Melvin said. "But I think they're all good Major League guys that can pitch late in games. I think all of them have the ability to close. I think as far as the depth they're all really good arms, but all of them have had struggles.

Entering Sunday's game, the bullpen was eighth in the NL with a 4.03 ERA and had converted 61 percent of its save chances.

Last year, the bullpen finished seventh in the NL with a 3.95 ERA and converted 77 percent of its save opportunities.

The struggles have emboldened those who were unhappy the D-backs traded closer Jose Valverde to the Astros in December. In return, the D-backs got Chad Qualls, who recently assumed the closer role, infielder Chris Burke and Minor League pitcher Juan Gutierrez.

Qualls looks like a keeper and is under club control for the next few seasons, while Burke has struggled mightily on offense and Gutierrez was 5-11 with a 6.09 ERA for Triple-A Tucson.

Valverde, meanwhile, is 5-3 with a 3.42 ERA and 42 saves in 48 chances for the Astros. Last year he was 1-4 with a 2.66 ERA and had 47 saves in 54 opportunities.

Brandon Lyon had some success in the closer's role for the D-backs this year, but had a miserable August and first part of September and was demoted to a setup man Sept. 13.

Since that time, Lyon has thrown three scoreless innings and allowed one hit in three appearances.

"I think you've seen a more aggressive guy," Melvin said. "It just looks like he's more confident and more aggressive."