"Philip is a great, great challenge each time you play against him. He's extremely smart, he's crafty in getting them in and out of the right plays. I think he's extremely tough in the pocket. He's going to stand in there and take his shots. And then he's going to get the ball out quick when he needs to as well.
"He is extremely accurate, he can make all of the throws, he's a great competitor and he's tougher than nails."
Zimmer hit on all of the reasons for Rivers' success.
"I knew he was an elite passer, but I didn't realize this was one of the smartest football guys in the NFL, bar none," offensive coordinator Frank Reich raved last year. "If there is a top 10 list of smartest guys in the league, he's on it, promise you. ... He just sees it faster than anybody else."
It's easy to forget that Rivers set an NFL record last season by generating a passer rating of at least 120.0 in five consecutive games. He's leading the league this season with an 81.2 completion rate and an 89.6 accuracy percentage.
When Rivers slumped in 2011, 2012 -- and again late last season -- it was due to subpar pass protection and/or injuries. As is the case with any great quarterback, however, he elevates the play of those around him when provided with a solid support system.
Among quarterbacks of his generation -- enjoying the prime years of their careers in the past decade -- only Manning, Brady, Brees, Kurt Warner and Ben Roethlisberger have played at a higher level.