He lauded the defense for forcing three turnovers (including his interception return for a touchdown) and holding the Broncos to season lows in total yards (407) and points.
But he also was critical of several costly defensive mistakes that ruined the Jaguars' chances of winning, mainly stupid penalties and failing to get off the field on third down.
While there were a lot of positives, the mistakes bother him more because they helped keep the Jaguars winless.
"We've got to take a really hard look at the type of mistakes we made," Posluszny said. "Early in the game we had them third-and-forever and they hit a checkdown, kind of a running back screen to get a first down. We're off the field on third down and all of a sudden we get a penalty.
"This is Peyton Manning of the Denver Broncos. You can't do things like that and expect to be successful."
There aren't moral victories in football, but what the Jaguars did defensively against the NFL's top team should qualify. The Broncos hadn't scored fewer than 37 points and had scored 52 and 51 points the past two weeks. But in the first half, the Jaguars held them to 14 points and 165 yards and frustrated Peyton Manning.
They forced two turnovers as well. Posluszny had the biggest play, picking off a Manning pass intended for Wes Welker and returning it 59 yards for a touchdown that cut the Broncos' lead to 14-12 with 36 seconds remaining.
"They ran a simple play-action and I had a guy running up the seam," Posluszny said. "I was able to read the quarterback's eyes, make a break on it, and get my hands on the ball.
"I just wanted to catch the ball and secure it first and then it opened up. Andre Branch makes a great block, make a cut off that, and we get to go. So that was great for us."
Posluszny described the play without a smile, strange because it was his first career touchdown. But he was so bothered by the mistakes the Jaguars made on what seemed to be every Broncos scoring drive that he couldn't enjoy it.
Manning converted a third-and-20 with a dump-down pass that running Knowshon Moreno took 28 yards to the Jaguars' 9-yard line. Moreno simply turned around and went straight up the middle of the field and got a couple blocks from receivers before cornerback Will Blackmon was able to drag him down. Two plays later they led 7-0.
The Jaguars stopped the Broncos on their next possession when Moreno caught a pass and gained just 4 yards on third-and-14. But Branch was penalized for unnecessary roughness.
The Broncos scored five plays later for a 14-0 lead.
The Jaguars held the Broncos scoreless on their next four possessions, ending one by recovering a Manning fumble and another with Posluszny's interception.
There were more mistakes in the third quarter. Safety Josh Evans was penalized for pass interference and unsportsmanlike conduct and safety Johnathan Cyprien was penalized for pass interference in the end zone -- all on Denver's first drive.
In Posluszny's mind, all those things ruined the things the defense did well, and coach Gus Bradley agrees.
"We celebrate the victories within the game," he said. "We celebrate the good things that took place. We're going to celebrate that we got a pick-six because we talk about that. Get the ball and score. That defines you as a defense. That's a good thing. We'll celebrate that. But the overall, the outcome that we're looking for, it's not where we want to be."