If you are losing, and you see your opponent is better than you on groundstrokes, there is something you can try. Volley aggressively, do it constantly, and commit to it.
Show your resolve.
If you get passed once, just dismiss the occurrence. Keep going forward, put the volley in the court, and keep the attacking attitude. More times than not the opponent starts missing passing shots or give you a few sitters that you can easily put away.
Realize that the match can start tilting in your favor. Keep up the pressure and the good works.
Oscar Wegner, TennisTeacher.com