Glennon's NC State team was thumped 34-0 by Florida State last season, and while Manuel wasn't interested in opening old wounds, he made a point to routinely mention the improvements the Seminoles' defense had made since then.
"He was saying how excited he was about their defense, and I was saying I was excited to go against them," Glennon said.
That enthusiasm hasn't waned in the months since, with Florida State's defense living up to much of Manuel's preseason boasts, and Glennon's arm accounting for 440 yards against Miami last week.
The friendly war of words hasn't diminished either. Manuel and Glennon have been friends since high school, growing up about 90 miles apart in Virginia, and they frequently exchange texts and phone calls during the season.
Last Saturday, Glennon fired off the opening salvo in preparation for this week's head-to-head matchup, predicting his Wolfpack would pull off an upset against Manuel's Seminoles, ranked No. 3 in the nation.
Manuel smiled, but didn't challenge Glennon's enthusiasm. He simply showed the text message to his teammates on Florida State's defense.
"It went over well," Manuel said.
It's not that FSU's defense is taking it too seriously. It's easy to lose track of the big picture when there's too much focus on one player. But Glennon's confidence has resonated with FSU's defenders.
"If he feels that way," said Lamarcus Joyner, "we'll see. I've made a lot of mistakes in my life by talking before the end result. But you definitely want to talk when it's over."
A little extra bulletin-board material should certainly spice up this week's game, but Florida State already knew the NC State quarterback would provide a challenge.
A year ago, Glennon struggled as his offense was shut out by Florida State. Afterward, he admitted he'd never seen a defense that played quite as fast as the Seminoles. This season, however, he expects to be far better prepared for the onslaught.
"You get another year under your belt with a guy that's that savvy, you're going to have to bring your 'A' game again," Jimbo Fisher said.
Through five games, Glennon is tied for second in the ACC in passing yards and his 10 touchdowns rank third. He held his own in last week's shootout against Miami, throwing four touchdown passes in a losing effort. He's a threat to go downfield, but he executes the short throws to his backs and tight ends with ease, making him the most dangerous pure passer Florida State has seen this season.
"He gets the ball out quick, and he's tall so he can see his receivers better," defensive tackle Anthony McCloud said. "He can kill us just by standing in the pocket, throwing the ball with accuracy."
The goal, McCloud said, is to get Glennon uncomfortable in the pocket with a strong pass rush, force him to move and wait for him to make a mistake.
For NC State, however, the challenge Manuel presents is just the opposite.
Indeed, Manuel has been dynamic in the face of pressure this season, completing 13 of 17 passes for 150 yards and two touchdowns when under duress.
NC State also got a firsthand glimpse last week of what might be in store Saturday when its defense allowed Miami's Stephen Morris to move outside the pocket with ease. Morris torched the Wolfpack secondary for an ACC-record 566 passing yards.
NC State responded with a players-only meeting this week in an attempt to regroup, but even O'Brien admits that some psychological damage already had been done, particularly in the defensive backfield, where All-ACC corner David Amerson was burned on five touchdown throws.
"It's a work in progress, and he's going to be challenged again," O'Brien said. "[Florida State] is a team whose wide receivers, from top to bottom, are as good as any team we play."
And Manuel is firing on all cylinders at the moment.
While Glennon is lauded for his ability as a pocket passer, no one has been more accurate than Manuel, who is completing a league-best 73.3 percent of his passes and owns a 176.6 passer rating that ranks eighth nationally.
Of course, Manuel isn't bragging about those gaudy numbers. His mind games with Glennon are more subtle.
"It's probably a silent rivalry," Manuel said. "I'm not going to be in his face. I want to beat him because he's our next opponent, but he's still my friend."
For the two seniors, however, this year's outcome will mark their final college matchup, which means the outcome will dictate the content of text messages for years to come.
"Obviously," Manuel said, "you still want to beat your friend when you get the opportunity."