Nyassi nailed home a low Khano Smith cross to record his second goal of the season. Mansally scored his first of the year from eight yards after a scramble in the penalty area.
It was Kansas City's first loss of the season after home wins against D.C. United and Colorado. New England, which beat Houston in its opener and fell to Chicago, improved to 2-1-0.
April 9 in Kansas City
Kansas City 1 New England 3
Goals: Jewsbury (pen.) 28; own goal (Jewsbury) 12, Nyassi (Smith, Mansally) 33, Mansally 40.
Kansas City - Hartman, Harrington (Myers 46), Conrad, Wahl (Colombano, 75), Leathers, Morsink, Zavagnin (Espinoza, 59), Marinelli, Jewsbury, Sealy, Lopez.
New England - Reis, Igwe, Parkhurst, Heaps, Smith, Joseph, Flood (Franchino 91+), Castro (Hilgenbrinck 66), Nyassi, Cristman, Kenny Mansally.
Referee: Terry Vaughn