Toronto also turned in an own goal on a shot originally struck by Russell Canouse, as D.C. became the 10th team in MLS history to score seven or more goals in an MLS match.
Kamara, Asad and Yow all scored in a nine-minute stretch after TFC defender Eriq Zavaleta received his second yellow card for pulling down Arriola, reducing the already well-beaten visitors to 10 men.
Ayo Akinola scored late in the first half for Toronto, which has lost six in a row while conceding 18 times in a stretch that now includes the largest defeat in club history
