Andrew Luck and Robert Griffin III went first and second overall in the 2012 NFL draft Thursday night— as expected. Then came the unexpected: a frenzy of trades that moved three teams up to make the next four selections in an entertaining first round.

In all, the round included 10 trades — the most since 2002, when 11 trades were made in the opening round.

An hour before the draft began, the Cleveland Browns pulled off a trade with the Minnesota Vikings to move up one spot from No. 4 and take Alabama running back Trent Richardson.

The Vikings, who originally held the third pick, took USC tackle Matt Kalil, giving second-year quarterback Christian Ponder the blind-side protector he needed. Then came two more trades, as the Jacksonville Jaguars moved up from seventh to fifth to take Oklahoma State wide receiver Justin Blackmon, and the Dallas Cowboys sent their first- and second-round picks to the St. Louis Rams to draft LSU cornerback Morris Claiborne sixth overall.

Those six players had long been considered the elite talents in the draft, but after Luck and Griffin, the order in which they would come off the board was anyone’s guess.

In recent years, running backs have rarely heard their names called early in the draft; last year only Mark Ingram (28th overall to the Saints) was taken in the first round. But Richardson, who last fall rushed for 1,679 yards and 21 touchdowns as the Crimson Tide’s workhorse back, frequently was predicted to be the exception this year.

Many analysts said he would be the first back taken in the top 10 since Darren McFadden went fourth overall to Oakland in 2008. But few — if any — expected him to go third overall. In the last decade, only two running backs — Reggie Bush at No. 2 overall in 2006 to the New Orleans Saints, and Ronnie Brown, also second overall, to the Miami Dolphins in 2005 — have been selected higher.

Counting the Redskins-Rams trade that saw Washington move from sixth to second overall, there were four trades among the first six selections — a rarity for the NFL, which in the last seven years witnessed only one such deal.

Some semblance of order was restored when the Tampa Bay Buccaneers took Alabama safety Mark Barron with the seventh pick and the Dolphins selected Texas A&M quarterback Ryan Tannehill with the eighth.

Four picks later, the Philadelphia Eagles moved up three spots — sending their 15th overall selection, as well as a fourth- and sixth-round pick to the Seattle Seahawks — to take Mississippi State defensive tackle Fletcher Cox. Later in the round, the New England Patriots traded up twice to take defensive end Chandler Jones out of Syracuse (21st) and Alabama linebacker Dont’a Hightower (25th).

Baltimore sent the 29th pick to Minnesota for the Vikings’ second- and fourth-rounders. Minnesota used that pick to take Notre Dame safety Harrison Smith. Denver later sent its 31st pick to Tampa Bay.

Thursday’s draft marked the 31st time, and the 10th time in the last 12 years, that a quarterback has been selected first overall.

It also marked the fifth time that quarterbacks have gone first and second. The last time was in 1999, when Tim Couch and Donovan McNabb went to Cleveland and Philadelphia, respectively.

Luck inherits the daunting task of replacing future Hall of Famer Peyton Manning, who spent all of last season recovering from multiple neck surgeries, restricted to the sidelines as the Colts went 2-14. During the offseason, Colts owner Jim Irsay fired team president Bill Polian, general manager Chris Polian and head coach Jim Caldwell and released Manning, who signed with Denver.

Now Irsay hands the keys to Luck, who transformed a struggling Stanford program into a contender, going 37-1 as a starter.

Luck said he can’t focus on trying to fill Manning’s shoes, however. “I couldn’t be more excited,” he said. “I’m not going to go crazy trying to do what Peyton Manning did . . . you obviously don’t replace him. You just do the best you can.”

Luck was the first of four quarterbacks taken in the first round. He, Griffin and Tannehill all went in the top 10, the second straight year that has happened. Oklahoma State’s Brandon Weeden went to Cleveland with the 22nd pick.

While Luck and Griffin are seen as near-can’t-miss prospects, Tannehill and Weeden face more questions thanks to the former’s inexperience and the latter’s diminishing youth.

Tannehill spent the bulk of his college career as a wide receiver before moving to quarterback, where he started 19 games. He endured a roller-coaster offseason, breaking his foot while training in January, and seeing his draft stock dip after he missed the Senior Bowl.

Following Tannehill’s injury, many projections had him going in the second round. But when the Redskins pulled off the trade for the Rams’ No. 2 overall pick, other quarterback-needy teams such Miami were more desperate and elevated Tannehill’s stock.

Weeden, meanwhile, offered experience, but a closing window of opportunity. The former New York Yankees pitching prospect went back to school after five seasons in the minor leagues.

Weeden will turn 29 in October, and some teams worried that by the time he developed mentally as an NFL quarterback, he would be past his prime.