I've witnessed the following during an officiated match. The players split sets. they were to play match tiebreaker. Both players took a break leaving the court. One player got back in about 2 minutes. At 2.45 the umpire started calling for the other player, warning that he has just 3 minutes for a break and must be on the court within 3 minutes. the other player showed up at like 3.30 mark, not even in a hurry or anything. He explained he just went to the bathroom and to get some water. The umpire called a game penalty on him. Since a match tiebreak counts as a single game, that was also a loss of the tiebreak, and loss of the match. There were some tears, explaining, but all in a very sportsmanlike fashion. the umpire just said these are the rules and that's it. He said if a player needed a bathroom break than he is entitled to it, and would get 'reasonable time allowance' - but the player must inform the umpire beforehand. the players shook hands and that was the end of it. Is that really the rule? is the 3 minute break rule written somewhere? how about a game penalty in this case - is that in the rulebook as well?