The Steelers considered DeCastro a steal with the 24th overall selection, a plug-and-play talent they could pencil in at right guard for the next decade. Beachum almost wasn't taken at all, a seventh-round flier who arrived in Pittsburgh as the fourth (and last) option at offensive tackle.
On Sunday, with the Steelers (7-6) clinging to their playoff lives in Dallas, the sure thing and the project will line up next to each other on the right side of the line.
And the weird thing is, Beachum will be the seasoned one.
The soft-spoken 23-year-old will make his third straight start against the Cowboys while DeCastro will make his regular-season debut after suffering a right knee injury in August that nearly cost him his rookie year.
If anything, Beachum's steady play has helped quell any butterflies DeCastro may have as his first start looms.
"Seeing how well (Kelvin) has fit in certainly gives me more confidence as well," DeCastro said. "I've waited a long time for this game, but that's life. Adversity comes along, but how well you can deal with it is the key to success. And I think I've dealt with it pretty well so far."
So has Beachum, who spent four years playing left tackle at SMU but figured there was no chance he'd hear his name called during the draft. He was so certain he would have to take his chances as a rookie free agent Beachum went to a family reunion on the draft's final day.
Driving back to campus, Beachum's phone buzzed and told him to hurry home. A short time later Steelers general manager Kevin Colbert called and urged Beachum to get packing after Pittsburgh took him with the team's final pick, No. 248 overall.
Eight months later, the 6-foot-3, 306-pound kid with the boyish face will line up in Cowboys Stadium—about 90 minutes north of his hometown of Mexia, Texas—and see Dallas defensive end Marcus Spears on the other side of the line of scrimmage.
Pretty heady territory for a kid who grew up in a school of 600 students simply hoping to land an athletic scholarship, though Beachum insists he won't be overcome by the moment.
Yeah, it's the NFL. It's still just football.
"They get paid just like you get paid," Beachum said. "They might get paid a little more, but you need to go out there and perform and put your best foot forward."
Something Beachum has done since being pressed into service following injuries to Marcus Gilbert, Mike Adams and Willie Colon. Beachum made his first start in Baltimore two weeks ago and helped keep backup quarterback Charlie Batch out of trouble as the Steelers rallied for a season-saving 23-20 victory.
The going was significantly rougher in last week's 34-24 whipping by San Diego, though Beachum was hardly alone as the Steelers struggled to get anything going offensively until the game was well out of reach.
He expects to bounce back this week. Having DeCastro line up next to him won't hurt. Beachum joked the two were "making history" though the Steelers will settle for the rookies creating running room for backs Jonathan Dwyer and Isaac Redman.
Offensive coordinator Todd Haley just smiled when asked if he's ever been in a situation where the entire NFL careers of the right side of the line is a combined four games. It's not exactly the lineup Haley envisioned in August.
"We've been in some pretty sticky situations but that's kind of how this year has been for this group," Haley said. "We haven't always performed the way that we'd like or up to our abilities, but I do think that with some of the adversity we've had to face through some of these injuries, it's forced the guys to become extra cohesive and look out for our own."
DeCastro and Beachum will certainly be looking out for each other on Sunday as the Steelers try to build some momentum heading into a showdown with Cincinnati on Dec. 23 that will likely determine which team plays into January.
"We're great together," DeCastro said. "(Kelvin's) obviously a smart guy, and I think we'll work well together."
The Steelers need them to if they expect to play into January. All niceties aside, Beachum really is the last option. Gilbert is out for the season with an ankle injury, Adams—the team's second-round pick in April—is out indefinitely with his own ankle problem and Colon is down with a balky knee.
Suddenly, Pittsburgh's Mr. Irrelevant is very relevant. Though Beachum understands he's unlikely to be the starter when everyone gets healthy, even if that's not until next summer, he doesn't try to think about what each snap means in terms of his future.
"You've got to man up, that's pretty much it," Beachum said. "It's simple man. You take it by the horns and you roll with it. You don't have time to think about what can happen, you've just got to block the guy in front of you."
NOTES: LB LaMarr Woodley practiced again Thursday and appears ready to start in Dallas. Woodley has missed the last two weeks with a sprained ankle ... LB James Harrison missed his second straight practice with an illness ... S Troy Polamalu also skipped practice but it was deemed "not injury" related. ... The Cowboys (7-6) are a game behind the Giants in the NFC East.
Follow Will Graves at www.twitter.com/WillGravesAP