Kamara's kick deflected off Toronto midfielder Andrew Wiedeman and through the fingers of goalkeeper Milos Kocic and into the bottom right corner of the net as Kansas City (14-7-4) won its third straight MLS contest.
''It's one of those set pieces that's not something that we crossed in and we finished it,'' he said. ''It's one of those where ... I tried to hit it on frame, and it took a perfect reflection for it to go to the back of the net.''
Sporting leads the Eastern Conference and is unbeaten in five straight games with the playoffs about a month away.
''We're just feeling it,'' said Kamara. ''We're top of the conference and we know if we keep playing our game thing are going to go our way. We want to finish the season being top of the league, and that's a goal.''
Toronto (5-14-5), which has had trouble with dead balls and giving up late goals, remained last in the Eastern Conference and extended its unbeaten streak to four matches.
''That's been the story of the season,'' Toronto defender Darren O'Dea said. ''We should have taken a point against a very good team. We've come away with nothing again and obviously it's disappointing.''
Toronto came out strong in the second half as Eric Hassli immediately went to work fighting off defenders and battling for possession in the box only to be shown a yellow card for his tenacious efforts.
He nearly scored in the 54th with a flick off Ryan Johnson's cross, but the ball rolled a foot wide of the right post. Johnson headed a pass from Torsten Frings slightly over the crossbar in the 70th minute.
The game got off to a chippy start with two yellows in the first 15 minutes. Frings earned a yellow card in the eighth by tackling a driving Graham Zusi from behind. The resulting free kick was blocked.
Four minutes later Kansas City defender Aurelien Collin was shown a yellow for a bad foul, but Frings couldn't connect on the free kick from outside the box.
In the 19th Sporting defender Seth Sinovic fired an ambitiously long-range shot from outside the box that found a clear path, though Kocic proved up to the task.
Kocic made a dazzling save in the 30th off a blazing right-footed shot from Kamara and then four minutes later stifled a charging Teal Bunbury that had the crowd roaring.
Toronto had several corner kick chances toward the end of the first half and came close with Terry Dunfield's header that Nielsen tipped just inches over the crossbar.