SAN FRANCISCO -- With a dash of new blood and an emphasis on offensive depth, the Giants formalized their Opening Day roster Wednesday before their exhibition game against the A's.

Rookies Hector Sanchez and Dan Otero are among the 25 players named to the Giants' Opening Day roster, and newcomer Gregor Blanco was one of the players who forced his way onto the club with their play in Spring Training.

Sanchez, a 22-year-old who has risen rapidly through the Giants' system, will serve as the backup catcher to Buster Posey, back on the roster after missing most of 2011 with a broken left leg. The club showed confidence in him being its best choice by optioning Eli Whiteside to Triple-A and trading Chris Stewart to the Yankees.

"He's done a good job. He's earned this," manager Bruce Bochy said of Sanchez, who hit .383 with four homers while working with all the pitchers this spring. "I talked to [Whiteside], and Whitey understands. It's hard not to look at what he's done this spring and the job he's done behind the plate. We're a team that can use a little bit of offense, and we think he's going to give us that."

For Sanchez, a promotion to the Major League roster to start the season was not something he was envisioning coming into Spring Training. Having worked on his defense in winter ball, Sanchez was just focusing on what he needed to do to improve.

"It's amazing," Sanchez said. "I never thought I could make the team, so I came here to work on my defense and work on my offense and learn. ... I get the opportunity to catch the best pitching staff in the Major Leagues, so it's amazing for me."

Otero, a 27-year-old drafted in the 21st round in 2007, will join the team's bullpen as one of six right-handers in a group that begins with eight pitchers.

Other newcomers to the roster include right-handed reliever Clay Hensley, infielder Ryan Theriot and outfielders Melky Cabrera, Angel Pagan and Blanco, who impressed the Giants with a strong spring.

"He came in here and made the club," Bochy said of Blanco. "With the job that he did with the bat and defensively and running the bases, he gives us a weapon, another potential leadoff guy."

On the pitching staff, Tim Lincecum, Matt Cain, Madison Bumgarner and Barry Zito will hold down the rotation until Ryan Vogelsong gives them a fifth starter when he returns from the disabled list, scheduled for April 15. The veteran core of Brian Wilson, Sergio Romo, Jeremy Affeldt, Javier Lopez, Guillermo Mota and Santiago Casilla rounds out the bullpen.

The infield includes Brett Pill making his first Opening Day roster, joining Brandon Belt, Emmanuel Burriss, Brandon Crawford, Aubrey Huff and Pablo Sandoval. Nate Schierholtz rounds out the four-man outfield corps as the lone holdover from 2011, and it's likely he'll be the fourth outfielder with Huff getting most of the time in left field and newcomers Cabrera and Pagan set in right and center, respectively.

To get the roster down to the 25-man limit, the team optioned Whiteside and right-hander Steve Edlefsen to Triple-A Fresno and reassigned to Fresno infielder Joaquin Arias despite a strong spring, as well as outfielder Justin Christian and right-hander Jean Machi.

In addition, the Giants placed second baseman Freddy Sanchez (left shoulder) and left-handers Dan Runzler (left lat) and Eric Surkamp (left elbow) on the disabled list, retroactive to March 26. The DL stay for Vogelsong (lower back) is retroactive to March 27.

Bochy said the move to send Whiteside, the backup on the 2010 World Series championship team, to the Minors was "really difficult," but offense ruled the day on that decision.

"Whitey's so well thought of by all his teammates and by myself and the staff, but we do feel like we needed to add a little more offense," Bochy said. "We think Hector can provide that and can help us there, so we're going to look at him."

Everything the Giants have seen so far out of the Venezuelan catcher, they've liked. He skipped all the way up the system in 2011, starting at Class A San Jose, jumping right past Double-A and ultimately to the Majors, where he made his debut in July on the first of three trips to the big club.

Along the way, he batted .285 with 23 doubles, 12 homers and 84 RBIs in 98 games in the Minors while going 8-for-31 with a pair of doubles in his short stints with the Giants. His excellent spring was the clincher.

"We did contemplate going with three catchers for quite a while, but we decided we needed another guy on the bench to help us out more than a third catcher," Bochy said.

One of the beneficiaries of that approach was Pill, who had some time in the big leagues last year, but is starting off 2012 with the Giants in a reserve role that will include starts at first base against left-handers.

"He gives us a threat," Bochy said of Pill. "He did a nice job last year coming up, and he's got two good years under him, so he's a guy who will be looked at to help us out from the right-hand side."