The 49ers made sure to keep a key part of their vaunted defensive line Monday when the non-tampering window of free agency opened.

Soon after the franchise tag deadline close, sources told NBC Sports Bay Area's Matt Maiocco that Arik Armstead and the 49ers agreed to a five-year contract extension that could be worth up to $85 million. A mere hours later, San Francisco made a shocking move. 

NBC Sports Bay Area has confirmed the 49ers have traded defensive lineman DeForest Buckner to the Indianapolis Colts for the No. 13 overall pick in the 2020 NFL Draft. ESPN's Adam Schefter reported Buckner and the Colts already have agreed to a massive contract extension. 

The front office's decision to move Buckner will frustrate plenty of fans, but both he and star tight end George Kittle were set to hit the open market after this upcoming season. And the 49ers have to re-sign Kittle. More than anything, the move completely alters the 49ers' game plan for the draft. 

Entering Monday, the 49ers owned the No. 31 overall pick in the draft. After that, they aren't scheduled to be on the clock until the fifth round. As Schefter noted, the NFC champions are in prime position to trade one of their first-round picks to gain more draft capital

 

But let's say they hold on to that No. 13 pick. The 49ers now are in great spot to address an area of need on a cheap rookie contract. 

If the 49ers want to address their new Buckner-sized hole, they can eye South Carolina defensive tackle Javon Kinlaw, who dominated the week of Senior Bowl practice. Kinlaw reached his potential as a senior, recording six sacks, though his tape and traits are more dominant than his stats. With Armstead's ability to play outside and inside, the 49ers possibly could look at an edge rusher like LSU K'Lavon Chaisson as well.

It's no surprise that the 49ers defensive backs have some question marks going into the offseason. Safety Jimmie Ward is a free agent, star cornerback Richard Sherman is turning 32 years old while entering the final year of his contract and they don't have a proven corner opposite of Sherman. 

The 49ers now can address their DBs early, especially after the Arizona Cardinals reportedly acquired three-time All-Pro receiver DeAndre Hopkins from the Houston Texans on Monday. Alabama safety Xavier McKinney seems perfect for defensive coordinator Robert Saleh, and Florida cornerback C.J. Henderson showed out at the NFL Scouting Combine. 

What this trade really does, though, is give the 49ers the chance to draft a star receiver in a class full of studs. 

Nothing is guaranteed, especially in the draft, but there's a good chance Oklahoma's CeeDee Lamb or at least one of Alabama's Jerry Jeudy-Henry Ruggs duo will be available. Somewhere, Kyle Shanahan is smiling with Tha Carter II on in the background.

Lamb, who feels like Hopkins 2.0, or Jeudy would give Shanahan a route-running extraordinaire to pair with Deebo Samuel's versatility. Either prospect can step in and be a No. 1 from Day 1. 

And then there's Ruggs. Shanahan dreams of speed like what Ruggs brings. The former Crimson Tide burner ran a 4.27 40-yard dash at the combine, where the 49ers just happened to meet with him. 

[RELATED: Report: 49ers likely to shop one of their two first-rounders]

The 49ers passed on signing Tom Brady in free agency, and are sticking with Jimmy Garoppolo to run the show. Shanahan and general manager John Lynch now are in perfect position to get their QB the target he badly needs to make another Super Bowl run. 

With Buckner becoming a Colt, the 49ers' draft plan completely changed.