Conceding three times in eight minutes to close the first half sent TFC to its fourth-straight loss in Kansas City.
An otherwise bright opening quarter-hour vanished when a deflected corner set up perfectly for Sporting Kansas City's Kei Kamara in the 28th minute. Kamara's acrobat scissor kick left Stefan Frei rooted to give the home side the lead.
The Sierra Leone international made it 2-0 less than five minutes later when he rose alone at the back post to nod a header past a helpless Frei to double the advantage.
With the wheels all but off at that moment, Kansas City's newest designated player, Jeferson, orchestrated a through-ball in behind TFC's rattled defence to Omar Bravo who danced around Frei to complete the first-half performance.
Making multiple changes to the lineup that fell 1-0 to FC Dallas midweek, Aron Winter will lament a number of missed opportunities that could have changed the entire complexion for Toronto before the 10-minute mark.
The visitors looked the better side to start the match and should have led on three minutes when a point-blank effort from Danny Koevermans was deflected over the bar by Sporting's Jimmy Nielsen.
Koevermans came close minutes later when he latched on to a Torsten Frings chip only to see his half-volley from the corner of the penalty area drift wide.
The Dutch import managed to pull one back for the Reds just after half time when Ryan Johnson's cross found the target man alone for a header at the back stick. But the comeback was short-lived as Kansas City answered through Bravo from a low cross in the 64th to make it 4-1.
Bravo's brace brought TFC's goals against number to 41 this season -- the total number the Reds conceded through all of last year.
Winter's frustration was obvious at the end of the first half when he replaced Santos with academy product Matt Stinson. Seeing enough of the Santos after the Brazilian carelessly gave up possession on multiple occasions in the opening half, Santos struggled in a midfield role just behind Toronto's three attackers.
Johnson improved the wide-open affair to 4-2 a quarter-hour from time when a mistake in the centre of Sporting's defence led to an easy finish for the Jamaican on a breakaway.
The Reds were without Terry Dunfield and Julian de Guzman who were questionable coming into the match, and Joao Plata failed to make the trip because of issues with his passport.
Bringing on three academy products to close out the match, the conditions and scoreline led Winter to use precaution and rest players before TFC's CONCACAF Champions League first-leg match against Nicaragua's Real Esteli Wednesday night at BMO Field.
Sporting Kansas City remained unbeaten in 12 league matches and perfect at brand new Livestrong Sporting Park.
Toronto continued its road woes and remained winless on the road in 2011.