McIlroy began the final round three shots off the lead and closed to within a shot of eventual winner Patrick Reed after two holes, but faded badly with a closing 74 at Augusta National.
And although it was not the collapse of 2011, when he enjoyed a four-shot lead after 54 holes before crashing to a closing 80, the Irishman has now failed to convert his first four chances to join Gene Sarazen, Ben Hogan, Gary Player, Jack Nicklaus and Tiger Woods in winning all four majors.
“I was surprised and I expected a lot more from Rory,” former Open champion Duval said. “It goes to show that nobody is exempt from the pressures and the crunch of trying to win major championships, let alone complete the career grand slam.
“This is going to be a tough one for Rory to handle and it’s going to keep stacking on as the years go by as he doesn’t win the Masters, and there is no one to say he will for sure.
“We all believe Rory will win the grand slam and I believe he can play this golf course, and I believe he will one day win on this golf course, but it doesn’t mean he will.”
McIlroy escaped with a par after a wild drive on the first and birdied the second after missing from four feet for an eagle, but was left to rue dropped shots on the third and fifth which killed any momentum.
“I think Rory chose the wrong club off the third tee too,” Golf Channel analyst Duval added. “With his power he should have just hit it right down in front of the green because that’s going to assure you of making a par.
“When he spun his wedge off that third green, he’s chipping from where he would have driven the ball. He didn’t take advantage of what he does best, which is drive the golf ball.”
McIlroy’s tie for fifth means he has finished in the top 10 at Augusta for the last four years, although this was the first time he was truly in contention.
“I can’t give a good answer as to what I can take from this into the future because I’m just off the 18th green, but I’ll sit down and reflect over the next few days and see what I could have done better,” the 28-year-old said.
“Whether it be mindset or whatever, I just didn’t quite have it today.
“I think when you’re playing in the final group in a major there’s always going to be pressure, but when I parred the first that settled me down so it wasn’t as if nerves got to me. I just didn’t quite have it.”