The 18-year-old caused Chievo's defenders a whole host of problems before getting his name on the scoresheet in the second half to seal all three points after Antonio Candreva scored an early opener.
Keita left the field to applause from both sets of fans having helped lift Lazio back into the hunt for a top-five finish.
Lazio raced into the lead with Candreva meeting Keita's cross from the left to beat Christian Puggioni from close range.
Candreva went close to making it two when his free-kick took a deflection on its way to clipping the top of the crossbar, but Chievo responded well to force Lazio onto the back foot.
This did not seem to concern the Biancocelesti too much, however, as they had the lively Keita as an outlet, and he showed all of his pace and skill to ensure Lazio were always a threat on the counter-attack.
He went close to doubling Lazio's lead in the 34th minute, but Puggioni managed to block his effort and there were no takers for Candreva's cross.
Lazio continued to play counter-attacking football which was proving more effective than Chievo's more persistent efforts and, from one of these breaks, Lazio doubled their lead.
Keita cut in from the right and shot low with his left foot, the ball taking a deflection off Michele Canini on its way past Puggioni.
Seven minutes from time, Lazio coach Edy Reja took Keita off and he earned applause from all corners of the Stadio Marc'Antonio Bentegodi with even the home fans recognising the impact he had made on the game.
Indeed, there was no way back in it for the Flying Donkeys, who remain just above the relegation zone together with Bologna while Lazio move above AC Milan and into the top half of the table.