His first pass ended with tight end Todd Heap fumbling. His second drive began with the Ravens backed up at their 3.
After Clayton took Derrick Mason's flip on a double reverse, Flacco hit the Bengals' Dhani Jones twice, knocking the 6-foot-1, 240-pound linebacker to the ground. That freed Clayton to race down the left sideline for a 42-yard touchdown.
"I'm supposed to block, but I really think I'm just supposed to not mess anything up and get in the way," Flacco said. "So I don't know what I was doing there. It was pretty exciting."
The Ravens supported Flacco with 229 rushing yards and a dominating defensive effort. But they also stumbled at times.
There were five dropped passes, including one by Heap in the end zone.
The impressive part was Flacco never seemed to blink.
"Joe was unbelievably poised," Clayton said. "For me, I don't consider him a rookie quarterback. He prepared well, and he came out here and he was ready to put us in a position to win the game."
Said Mason, "He is starting to really come into his own right now."
Still, the Ravens realize there is a learning curve for Flacco.
He just happened to pass the first test.
"This was the beginning for Joe," Harbaugh said. "Now we've got an idea of where he's at, and what he needs to do is get better. He played well, but he needs to take this week to next week and make the most improvement maybe he will ever make in his career. That should be his goal."
So, will Flacco be the starting quarterback for now?
Harbaugh quickly replied, "We'll see."
Flacco firstsCompletion: A 9-yard pass to tight end Todd Heap, who fumbled on the second play of the game for the Ravens, just 47 seconds into the game.
Incompletion: With 11:24 left in the first quarter, Derrick Mason dropped a pass at the Ravens' 15-yard line that would have given them a first down.
Touchdown: A 38-yard run with 15 seconds left in the third quarter on a bootleg. Flacco was supposed to hand the ball off but saw that the play would not have worked, so he kept it and took off for the end zone.