In his 2nd hand match with Stanislas Wawrinka at the 2012 Australian Open, Marcos Baghdatis was down 2 sets and on the way to losing the match in the 3rd set. To vent his anger and frustration he smashed the racquet he was using on the ground, and then broke a further 3 racquets which were in his bag.
This seemed to help, as he eventually won the 3rd set 7-5. He then however only won 1 game in the 4th set, and Stanislas Wawrinka won 7-6 6-4 5-7 6-1.
See http://www.youtube.com/watch?v=DnKfCPF6s4o for the action filmed from a different angle.