Tennis matches can be long, physically challenging affairs. Matches are often determined by the serving proficiency of the players. The serve has been extensively studied, but the relationship between the serve and match length regarding knee kinematics and leg muscle activation is not well documented in a real time environment. The purpose of the current study was to determine the effect a three-set tennis match had on knee kinematics and muscle activation of quadriceps and hamstrings during the serve. Ten male collegiate tennis players (age:​ 19.6±1.7) were recruited from The University of Texas at Tyler. All participants played a three-set match and digital video recordings and electromyography (EMG) readings of the first five serves (Test 1) and last five serves (Test 2) from each set were taken. Motion capture analysis was performed to calculate knee flexion and angular velocity. EMG analyses of selected muscles were performed through root mean square (RMS) and median power frequency (MPF). Significant test differences were seen in knee flexion and RMS values for the biceps femoris. Set differences were observed for the RMS values of the rectus femoris and both the RMS and MPF values of the biceps femoris. Additionally, a set by test interaction for the RMS of the rectus femoris was observed. Knee flexion results are consistent with previous studies which have shown that decreasing knee flexion has a detrimental effect on the serve and can cause a reduction in efficiency to occur as well. Recommendations to coaches would be to cue the players in on their legs during the serve when a decrease in proficiency occurs during a match.