PITTSFORD — Doug Marrone told us it was only a matter of time before the “separation” became evident in the battle for the Bills’ No. 1 quarterback job between rookie EJ Manuel and Kevin Kolb.

On Sunday, the separation was total. Kolb was nowhere to be seen. The veteran had twisted his left knee by slipping on the mat between the two practice fields the day before. So Kolb was held out of Sunday afternoon’s practice session at St. John Fisher College.

Reporters asked throughout the day to speak with Kolb, but the team said he was getting treatment. Maybe he was still trying to calm down. Kolb tossed his helmet in dismay after getting hurt. No athlete likes to suffer a fluke injury, especially one with a reputation for getting hurt.

It was also the predictable reaction of a player who had not performed well in his first week of training camp and realized that any time lost in workouts might compromise his chance of winning the job.

Kolb didn’t distinguish himself in the first week at Fisher. He missed some easy throws and held the ball too long at times. He displayed many of the flaws that caused his previous teams to give up on him. One media regular said Kolb has looked like “a poor man’s Ryan Fitzpatrick.”

So this was a great chance for Manuel to assert himself and create some separation. Manuel had been the better man in the first six days. He was surprisingly accurate, much more poised than in minicamps, when he struggled and made it seem the job was Kolb’s to lose.

For most Bills fans, I imagine, this was a blessing in disguise. Getting Kolb out of the way could only hasten the process and nudge Marrone to make the inevitable call: Give the starting job to the prize first-round pick, the franchise guy, and let the future begin.

Manuel got all the first-team snaps in team drills. An enthusiastic crowd watched from the stands at the grass field inside the Fisher track. It was EJ’s time to shine … and he was terrible.

It was Manuel’s worst day of camp. On a windy afternoon, against Mike Pettine’s attacking first-team defense, Manuel was intercepted three times. He looked like a raw rookie on the last one, locking his eyes on tight end Lee Smith and throwing the ball right into the arms of rookie linebacker Kiko Alonso.

“The production end I agree with,” Marrone said when told it was not one of Manuel’s better days. “But today was a great day for him. He did a lot of third down. Early on, I said we were going to progress him against all the looks. Obviously now, with Kevin not being there to practice, we’re throwing him in there.

“It’s always difficult. A poorly thrown ball, a tipped ball, a ball that a receiver should win on. I think you go through that process. The one good thing about it is, today was a third-down day and he got a lot of work against some tough looks.”

Those are the looks that separate quarterbacks in the NFL. Third down is when teams attack you from unexpected directions and force you to make quick decisions — and precise passes — in the blink of an eye.

Kolb has failed to do it in the NFL on a consistent basis. That’s why he’s a journeyman. Ultimately, his shortcomings will dictate the move to Manuel. His record shows he will give up sacks, fail to make big throws down the field and struggle to remain healthy.

Manuel has the advantages of talent and promise. He is an investment in the future. He has done well in camp.

But to this point, his perceived edge has more to do with Kolb’s failures than his successes. On Sunday, he didn’t have Kolb to make him look better by comparison.

Of course, it helps to remember that we’re only one week into camp. There’s been so much anticipation for this training camp, and so much excitement about Manuel’s long-term prospects. There’s a risk of making hasty judgments every time he or Kolb throws a football.

This was a welcome jolt of reality. Yes, Manuel has the physical tools. He has a big arm and dynamic running ability. He also showed great touch on a corner pattern to Fred Jackson for a touchdown in seven-on-seven drills.

It’s still early. Manuel had the upper hand on Kolb the first five workouts. The No. 1 job should be his if the competition is remotely close. But he’d been doing it in controlled settings. He was famous for looking great in the spring at Florida State, though it didn’t always translate in the fall.

The true separation is yet to come. Next Sunday, the Bills open their preseason at Indianapolis. Let’s see what happens against real opposition, against defenders with jobs to win and menace in their hearts.

“You can see part of the process is really until we get to that preseason game,” Marrone said. “That’s really what we’re looking for. It’s not something that’s going to be done beforehand. I don’t like to pass judgment or complete an evaluation until we go in there.

“Obviously, EJ hasn’t gone into that type of atmosphere,” Marrone added. “I just want to see how he looks and responds in that atmosphere.”

Manuel wasn’t available to the media after Sunday’s practice. I imagine he would have been more critical of his play than Marrone. He has a good head on his shoulders, and it was probably spinning after his first real look at Pettine’s third-down defense against the starters.

It will be interesting to see what happens in the first exhibition. Manuel has made strides since the spring. The minicamps were good for him. He seems to be a quick study, a willing student. Some of the rudiments of NFL quarterback play are clicking for him now.

You never know for sure until a guy does it against live competition — and in the regular season. Manuel has a lot to prove. But at this point, it hardly seems like any great achievement to beat out Kevin Kolb.