The experiment with 33 participants showed that the social relationship between players (playing a first-person shooter game against a friend or a stranger, and in single-player mode) influences phasic emotion-related psychophysiological responses to digital game events representing victory and defeat. Irrespective of opponent type, a defeat elicited increasing positive affect and decreasing negative affect (supporting earlier results), but it was most arousing when the opponent was a friend. Surprisingly, victory--in addition to positive emotion when playing against either human opponent--also elicited a negative response when the opponent was a friend. Responses to defeat in a single-player game were similar, but to a victory almost neutral. These results show that the social context affects not only the general experience, but also individual emotional responses, which has implications for adaptive game systems, experience research, and game design alike.