This will be Walker's first opportunity to play every day in the big leagues, and it comes almost exactly six years after the native Pittsburgher was selected by his hometown club as the No. 11 overall pick in the First-Year Player Draft.
"It's obviously something that I've dreamt about since I was a little kid," said Walker, who had hit safely in four of six games since being called up entering Monday's game against the Cubs. "I'm very happy and feel very fortunate for the opportunity. I'm going to go out and work hard and live up to this opportunity."
The irony in all this is where Walker will be playing. He was drafted as a catcher and worked exclusively behind the plate until the organization asked him to move to third base in 2007. Walker established himself as an above-average defensive player there for the next three seasons, but the arrival of Pedro Alvarez left Walker with little opportunity to play third for Triple-A Indianapolis this year.
As a result, the Pirates decided to groom him into a utility player. That began this spring and continued in Triple-A until his callup last week. It wasn't until Spring Training that Walker had ever taken a ground ball at second.
"When I was the kid, when I was younger, I played shortstop, pitched, played third," Walker said. "I never ever saw myself playing second base. Not in a million years."
Though Walker might still make a periodic spot start at third to spell Andy LaRoche, who is dealing with an ailing back, the 24-year-old can now focus his attention on his newest position.
He made one error in 21 Triple-A games there and has had one in four starts at second with Pittsburgh. The intricacies of the position, such as turning double plays and where to be on cutoff throws, still must be mastered. But the consensus is that Walker's athletic ability -- he was a multi-sport star in high school -- will help tremendously in the learning process.
"The more he plays out there, the better he will get," Russell said. "He does have a good glove. We saw that at third. I look forward to seeing him develop there."
"With all the work that I've gotten in a row, it feels a lot more comfortable," Walker added. "There's obviously a lot to be done and a lot more to be learned. I hope very soon to be as confident at second as I am at third. I don't think that's far off."
Russell continues to pencil Walker into the second spot in the lineup, though Russell noted that could change. The lineup shuffle will affect Andrew McCutchen as well, as the center fielder will permanently move back into the leadoff spot, which had belonged primarily to Iwamura.
As for Iwamura, he finds himself out of an everyday role for the first time since coming to the Majors. Since the start of Spring Training, the Pirates have talked about how a core of high-level Minor League players would push established starters out of jobs if players didn't perform. Iwamura, whom the Pirates traded for this offseason, becomes the first victim of just that.
"It's not an easy pill to swallow," Russell said. "I'm sure he's disappointed. I'm sure he's upset. Hopefully, he takes it the right way and works hard."
Iwamura, the team's highest-paid player with a $4.85 million salary this season, has struggled tremendously all year. His .173 season average, which recently included an 0-for-34 stretch, was the lowest among all National League starting second baseman. His .274 on-base percentage wasn't much better.
Defensively, Iwamura showed plenty of signs that his surgically repaired left knee was still a hindrance. He showed poor range and hesitancy when turning double plays.
The Pirates could release Iwamura, though doing so would leave Pittsburgh still on the hook for the remainder of his salary.
Jenifer Langosch is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.