American teenager Madison Keys was immersed in her algebra homework when she got the message that she was due on court in 10 minutes to play fifth seed and former French Open champion Li Na at the Madrid Open.

Lucky loser Keys quickly abandoned her books in the players' lounge as she made a dash for center court after being handed a place in the main draw following the late withdrawal of Tamira Paszek through injury.

With no time to dwell on what was happening, the 18-year-old from Illinois quickly dismantled fifth-ranked Li's game to secure a shock 6-3, 6-2 win for her first career victory against a top-10 opponent.