Swansea stunned European champions Chelsea in their English League Cup semi-final at Stamford Bridge to take a two goal advantage back to Wales for the return leg.
Michu scored his 16th goal of the season, and Danny Graham added a late second to put the Swans within touching distance of their first ever major Wembley cup final.
Fernando Torres started lively enough, drifting out to the left flank where he delivered a clever cross to the front post, but Branislav Ivanovic headed over. The Spaniard soon exhibited signs of his recent dip in form, however. He picked the ball up 30 yards out and crept towards goal before firing a wayward shot that cleared the bar by many metres.
The Blues dominated the game, but lacked a killer touch up front. A brilliant flowing move that included touches from Oscar and David Luiz eventually ended up with Ramires in space in the Swansea box but he could only prod weakly at Gerhard Tremmel.
Efforts from Cesar Azpilicueta and Gary Cahill both went wide while Juan Mata lost his usually clinical touch in front of goal after a foray in to the box by Eden Hazard. Another brilliant move came on the half-hour with Oscar backheeling the ball in to Mata from Ramires' pass, but once again the former Valencia man shot wide. Torres' only decent contribution of the opening 45 minutes came when he split the Swansea defence, but Tremmel came to the Swans' rescue.
A quiet hush fell upon Stamford Bridge, with the hosts' lack of penetration up front clearly dampening their enthusiasm. The most noise the home support displayed was when Lampard emerged from the dugout to warm up.
The Blues fans fell silent moments later, however, when Ivanovic's error gifted Swansea the lead. Jonathan de Guzman pinched the ball off the Serb as he dallied on the edge of his own box and squared to Michu, who calmly slotted the ball past Ross Turnbull.
Azpilicueta claimed Ben Davies had handled his cross in the Swansea box, but referee Anthony Taylor thought otherwise. Lampard could not remove his tracksuit quick enough when Benitez beckoned the midfielder over to tell him he wanted him to come on with 20 minutes to go.
Lampard adds vigour to Chelsea
Lampard injected life in to Chelsea, but Torres continued to perform poorly. The striker found space on the edge of the box, but could only head weakly in to Tremmel's arms.
Ki then sent Michu through with a clever pass, but the linesman flagged for offside just as the former Rayo Vallecano man was about to pull the trigger.
Benitez finally answered the home fans' demands and brought on Ba with nine minutes left. The striker made an immediate impact, going close with two efforts, the second a looping header from Marko Marin's cross.
Ba hurtled through in injury time and went down after Tremmel failed to collect the ball, but the referee did not give a penalty and instead booked the former Newcastle man for diving. Chelsea's night then turned worse with one minute of added time left. Ivanovic's second terrible backpass allowed Graham to pinch the ball off Turnbull before slotting in to an empty net.
Ba thought he had pulled one back for the Blues moments later but his effort was ruled out for offside.