Despite a rough camp, Rodriguez had been penciled in at the position mainly because he's the only left-handed starter remaining on the roster following Andy Pettitte's move to the Yankees.
After struggling with his location and walking a total of nine in his prior two starts, Rodriguez allowed 10 hits with two runs and no walks in six innings during Houston's 5-3 win over the Kansas City Royals.
"I had good location today and I threw a lot of strikes," he said. "Today I had to do it well because I had two bad outings."
Astros general manager Tim Purpura agreed, saying his work on Saturday was key in their decision-making.
"We were watching Wandy real closely and if he would have had scuffled today things could have been different," Purpura said.
Houston set its 25-man roster by purchasing the contracts of relievers Rick White and Brian Moehler from Round Rock and optioning pitchers Matt Albers and Fernando Nieve and shortstop Eric Bruntlett to the Triple-A team. The Astros also reassigned catcher Eric Munson to Round Rock.
Purpura said sending Bruntlett, who hit a three-run homer against the Royals, to the minors was the most difficult decision of the day.
"Eric Bruntlett's done a lot for this organization and this team," he said. "It's tough to have to send somebody like that down. He's an asset. He can help us win, it's just that we don't have a spot on the roster for him right now."
Chris Sampson was selected as Houston's fifth starter, but will be used in the bullpen early as a fifth starter won't be needed until April 10.
Sampson, who was out of baseball from 1999-2002, said his winding path to the majors makes getting the spot even more exciting.
"I took the unconventional way to get to the big leagues," an emotional Sampson said as his family cheered in the distance upon learning the news. "I've only been pitching for basically four years professionally after three years off. Who would have thought I would have even made it, much less be the No. 5 starter in the Astros rotation."
Sampson was 2-1 with a 2.12 ERA in 12 appearances, three starts for Houston in 2006.
Purpura said he leaned down as if he had been struck when told the news.
"I just told him, 'You deserve it. You've worked hard to get to this point," Purpura said.
Both Luke Scott and Jason Lane made the 25-man roster, but manager Phil Garner said Scott will start on opening day. Lane was replaced by Scott last season after Lane hit .205 in the first three months. Scott had 10 homers and 37 RBIs in 65 games after being called up from the minors after the All-Star break.
"I feel like Luke has earned the right to start on opening day," Garner said.
Garner said he will use Lane some against left-handed pitchers, but that Scott would get most of the starts.
Scott believes his late-season performance in 2006 helped him get the starting job.
"It did a lot in proving myself to those who had their doubts that I could do this on a big league level," he said.
On Saturday, Royals starter Brandon Duckworth allowed six hits and one run with three strikeouts in 4 1-3 innings. Duckworth is Kansas City's fifth starter.
"Brandon threw well," said Royals manager Buddy Bell. "I thought he had good command and threw good pitches for the most part. He really only threw one bad pitch, and that was a breaking ball up to Brad (Ausmus)."
A new sign that will count down Craig Biggio's quest for 3,000 hits has been added to an outfield wall at Minute Maid Park. The sign has 2,930 lit up in red, flanked by a pair of images featuring Biggio at the plate and the words "Career Hits" above the total.