Ryan Roberts was not in the Diamondbacks' original starting lineup Tuesday, only added when third baseman Melvin Mora was unable to go because of a sore foot suffered during the last homestand.

After the second two-home run game of his career in a 5-4 victory at Cincinnati, Roberts is making harder and harder for manager Kirk Gibson to exclude him. Roberts extended his hitting streak to six games, tying a career high, with homers in the first and fifth innings, and he also walked and stole a base in the seventh inning. He has four homers and two steals this season.

"He's earned the right to play, for sure," Gibson said.

Roberts had a single while starting at second base to give Kelly Johnson a day off Saturday, and he had two hits, including a game-tying single with two outs in the eighth inning, while filling in for Mora on Sunday. Roberts has made seven starts at third base (Mora had the flu earlier) and one at second, and he finished a game at shortstop last week. Roberts also has major league experience in left field in 2009-10.

His first homer Tuesday, off Cincinnati right-hander Sam LeCure on a 2-0 pitch, was a solo shot to right field, and his first-pitch, two-run homer to left in the fifth gave the D-backs a 4-3 lead.

"After the homer to right, I thought he might pitch me in. I guessed right. It was a fastball middle-in, and I just happened to hit it," Roberts said.

Roberts hit .506 this spring but was not guaranteed a roster spot until Geoff Blum was placed on the disabled list with a right knee injury to open the season.

"To come in and put a uniform on is great. To have a start like this, you want to keep working," Roberts said.

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