Klitschko dropped Brock with a huge right cross to the jaw yesterday. The American rose to his feet at the end of the count but was so wobbly, referee Wayne Kelly waved an end to the scheduled 12-round bout at 2:10 of the seventh.
Klitschko, 30, improved to 47-3 with 42 of his wins coming within the distance.
The 31-year-old Brock, a member of the 2000 US Olympic boxing team, suffered his first defeat after winning his opening 29 professional bouts.
Klitschko was making the first defense of the IBF and International Boxing Organisation (IBO) crowns he won by stopping American Chris Byrd in the seventh round last April in Mannheim, Germany.
Klitschko came alive in the seventh after sustaining a cut over his right eye in the middle of the sixth.
The 6-foot-6 Klitschko showed his fire, setting up the final knockout shot with a left hook, hard right combination. He followed that with a sharp jab and devastating right to end the bout.
''It was a left hook, straight right combination,'' Klitschko told reporters. ''I should have landed it that way earlier in the fight. But it took that much time to get my rhythm and distance.
He's a good defensive fighter.
Klitschko said the cut, which left blood trickling down his face in the sixth round, was from a head butt.
''I made the mistake of getting too close,'' said the champion, who enjoyed a four-inch height and reach advantage.
''He had a better jab than I thought he did,'' Brock said of the champion's primary weapon before the onslaught of big rights in the last round.
''I saw the punch coming but I couldn't react fast enough.
He's really good. He's strong.'' The fight was fairly even heading into the seventh, with Klitschko using his stinging jab and Brock countering with sharp left and right hooks to the body.
Klitschko, who also held the World Boxing organisation heavyweight title from 2000 to 2003, weighed in at 241 pounds.
Brock tipped the scales at 224.
The champion said he was eager to consolidate the heavyweight division, which has four title holders including WBC champion Oleg Maskaev, WBA title holder Nikolai Valuev, and American Shannon Briggs, the WBO champion.
''I will fight anybody with a title,'' Klitschko said. ''I want to fight someone with a title.'' REUTERS SAM RN1135