Quinn didn't have enough time.
He led the Chiefs to a field goal on his only series, but the Chiefs defense couldn't get the ball back in the closing minutes, allowing the Ravens to hold on for a 9-6 victory.
"If we will play like that going forward, we give ourselves a chance to win the game," Chiefs coach Romeo Crennel said. "We had a chance in this game. So even though I'm disappointed in the loss, the way the team played, we played much better overall football."
That wasn't necessarily the case for Cassel, who threw for just 92 yards and was picked off twice along with being credited for two lost fumbles.
His day finally ended when Ravens defensive tackle Haloti Ngata got to him in the fourth quarter, hitting him just as he released a completed pass to Jamaal Charles out of the backfield.
Fans have been calling for Cassel to be benched for several weeks, and certainly have been dissatisfied with his performance for longer than that. He was booed during a celebrity softball game across the parking lot at Kauffman Stadium during Major League Baseball's All-Star festivities.
The fact that some of them cheered when he got hurt didn't sit well with the Chiefs.
"It's 100 percent sickening," right tackle Eric Winston said. "If he's not the best quarterback, he's not the best quarterback, and that's OK. But he's a person. And he got knocked out in a game and we've got 70,000 people cheering that he got knocked out."
Jamaal Charles, who had 140 yards rushing in the game, said, "It's just not right."
It's unclear how long Cassel will be out, but at this point every indication is that Quinn will be the starter when the Chiefs head to Tampa Bay next weekend.
Justin Tucker made all three of his field goal attempts for Baltimore (4-1), bailing out an offense that struggled much of the afternoon. Ray Rice ran for 101 yards, but Joe Flacco had just 187 yards passing and was intercepted once.
"They're a good defense," Flacco said. "I remember that from two years ago when we came here for the playoffs. We never really got in a rhythm the first half. The second half, I thought we played pretty good. We just didn't capitalize in the red zone."
Kansas City (1-4) spent most of the first half handing off to Charles and backup running back Shaun Draughn, doing everything in their power to keep from having to make Cassel win the game.
Charles responded most of the first two quarters, routinely gashing the Ravens defense for big gains. He had 125 yards rushing at halftime, more yards than Baltimore had as an offense.
Baltimore took advantage of the Chiefs' first turnover when Tucker connected from 28 yards out with 1:21 left in the first quarter, but Ryan Succop's 30-yarder sent the game to halftime tied 3-3.
Kansas City had a chance to pull ahead after Baltimore fumbled the opening kickoff of the second half. Pass interference gave the Chiefs the ball at the 1-yard line, but Cassel fumbled the snap and Reed recovered it, keeping the game tied.
Tucker added a 26-yard field goal moments later, and after Cassel was picked off on a pass that bounced off Bowe's helmet, Tucker hit again from 39 yards to make it 9-3.
Cassel was hurt midway through the fourth quarter. Quinn entered the game and thought he'd given the Chiefs the lead when he found Dwayne Bowe for a would-be touchdown, but Dexter McCluster was called for pass interference and the Chiefs had to settle for another field goal.
Flacco scrambled for 16 yards on third-and-15 with a couple minutes left in the game, and Rice plunged for another first down with just over a minute remaining to help run out the clock.
"We play a team game. It's offense, defense and special teams, and I need all of them clicking to make it happen, and they didn't click enough to make it happen today," said Crennel, now 27-45 as an NFL head coach. "If the defense clicks like it did today, we'll have a chance."
Notes: Chiefs LBs Justin Houston and Tamba Hali each had two sacks. ... Kansas City has been outscored 44-6 in the first quarter this season. ... Quinn was playing for the first time since Dec. 20, 2009, with Cleveland. ... The Ravens had 298 yards of offense. They're averaging 310.5 yards in two road games and 457 yards in four home games.