"I'm just really, really disappointed in myself right now," he said at his post-game press conference.
Romo's most costly interception, a 34-yard pick-six by cornerback Bruce Johnson, came on third-and-10 in the first quarter. The play showcased Romo at his pre-snap best and his post-snap worst.
More Anatomy of a Play: Romo's good side
The Cowboys aligned in a spread formation with Romo in the shotgun. Initially, the Giants were showing a Cover 2 defense, with two deep safeties. But as Romo began his cadence, the Giants tipped their hand that they were not playing Cover 2. Safety Michael Johnson and linebacker Antonio Pierce approached the line of scrimmage, indicating a blitz was coming.
Romo saw the imminent pressure and audibled to a play that would protect him and give him a place to throw the ball against man-to-man coverage. It was a great check by Romo.
Pierce wisely cancelled the blitz and audibled to a basic Cover 2 zone defense.
Romo's interception was a result of Pierce's outstanding audible and Johnson's precise execution of the Cover 2.
Johnson was responsible for the underneath zone to Romo's right. Dallas' route combination called for the outside receiver, Roy Williams, to run directly at Johnson for 5 yards and then cut in. The inside receiver, Patrick Crayton, was running a 12-yard bow-out behind Johnson. Williams' route was meant to hold Johnson short, so Romo could complete the first-down throw to Crayton.
Johnson's awareness of what he was seeing was rare and surprising, for a rookie. He recognized the route combination instantly and played it perfectly. He covered Williams just long enough to make Romo think Crayton was open.
Just as Romo delivered the ball, Johnson dropped off of Williams' route to get under the throw to Crayton. Romo saw Johnson's adjustment too late. Only after he let go of the ball did he realize he had been suckered by the undrafted rookie free agent.
Interceptions will happen -- defensive coaches and players get paid, too. This was a case where they earned their money and mentally broke down one of the most decisive quarterbacks in the NFL.
"You can't make that mistake," said Romo. "That's the bottom line. When you do, it costs your football team, and it cost us tonight".