SURPRISE, Ariz. -- Matt Harrison, answering the challenge issued by C.J. Wilson on Tuesday, was outstanding on Thursday night. The battle for the fifth spot in the rotation continues to heat up.

Or there could be two openings in the rotation depending on what happens with Tommy Hunter.

Hunter has always been considered the leading candidate for the fourth spot, but he was scratched from Thursday's start against the Brewers with a strained intracostal muscle in the left side of his rib cage.

Hunter said he strained the muscle throwing his changeup during his pregame warmups in the bullpen.

"I was feeling strong in the bullpen," Hunter said. "Throwing great. I was spotting a perfect game, a no-hitter in the bullpen. Then I went, 'Oh poop,' and said all kinds of choice words."

If Hunter is the fourth starter, he would make his first start three weeks from Friday against the Seattle Mariners at the Ballpark in Arlington. But so far he has made just two starts in the Cactus League, pitching a total of five innings and posting a 1.80 ERA.

"The way things are in Texasland, if you go down, you might not have a job," manager Ron Washington said. "But our concern is for Tommy."

This is the second straight spring that Hunter has been hit with an injury. He was sidelined last year with a strained groin muscle and pitched just six innings. He started the season in the Minor Leagues before spending the final three months in the Rangers rotation.

He was 9-6 with a 4.10 ERA in 19 starts and that's why he came into camp as the leading candidate for the fourth spot. He was also off to a strong start before being scratched on Thursday night.

"It's an unfortunate thing that happened," Hunter said. "I don't know what to tell you. I'll get out there as soon as I can."

Wilson pitched against the Cubs on Tuesday and allowed just one run in four innings while receiving rave reviews. Harrison answered back on Thursday.

"C.J. did a great job," Harrison said. "He's pitching his tail off. Everybody on the staff is trying to win a spot. He's helping his cause and I'm trying to do the same thing, and be as good or better than the next guy."

Harrison, scheduled to pitch four innings, entered the game in the fifth and Guillermo Moscoso and Willie Eyre got through four. Harrison gave up an infield single to start his night, then retired nine straight hitters. Seven were on strikeouts, including five in a row.

"It was pretty fun," Harrison said. "I usually don't get many strikeouts. It was pretty exciting to get that many strikeouts in a row. But some of those strikeouts were on 3-2 pitches. I ran my pitch count more than I wanted to."

He did walk the leadoff batter in the eighth, his last inning of work. That led to a couple of runs when on a bloop double to right and another double that grounded inside the third base bag. The leadoff walk was the only sin on another superb outing. For the spring, Harrison has a 2.00 ERA. In nine innings, he has allowed two runs on eight hits, one walk and 10 strikeouts.

The pitching competition is fierce. Hunter can't afford to miss time.