Complex sentence: At the 2009 Monte Carlo Masters, Wawrinka defeated World No.2 Roger Federer in straight sets, an upset which halted the chance of a fourth straight Nadal-Federer final in Monte Carlo.
Split into simpler sentences: At the 2009 Monte Carlo Masters, Wawrinka upset World No.2 Roger Federer. Wawrinka's straight sets victory over Federer halted the chance of a fourth straight Nadal-Federer final in Monte Carlo.