Sporting Kansas City stunned Philadelphia Union in a penalty shoot-out to lift the US Open Cup, American soccer's oldest competition.

Spanish youngster Jordi Quintilla fired the winning spot-kick for Kansas to clinch a 7-6 victory after the two sides finished deadlocked at 1-1 after extra-time.

It was another agonising defeat for Philadelphia who also lost last year's final in front of their home fans.

The Union had taken the lead through striker Sebastien Le Toux in the 23rd minute, the Frenchman latching on to a long pass from compatriot Vincent Nogueira and finishing past Kansas goalkeeper Tim Melia.

Union had several chances to extend their lead through the remainder of the first half but an inspired goalkeeping display from Melia kept them at bay and allowed Kansas to stay in the contest.

Kansas improved in the second half and looked the likelier team to score as nerves appeared to get the better of Philadelphia.

They grabbed a deserved equaliser in the 65th minute through Hungarian striker Krisztian Nemeth, curling in a low shot from the edge of the area.

Neither side was able to grab a winner in extra-time and when substitute Andrew Wenger saw his kick saved by Melia, Quintilla stepped up to calmly roll home the winning penalty.