TENNIS buffs who paid to watch the Richard Ellis Challenger finals yesterday spent most of the afternoon watching enthusiastic young boys and girls mopping up the Victoria Park Centre Court. The ball boys and girls were out in force drying up the court with towels and mops when the rain ceased, but no sooner had the players prepared to start than the rain fell again. The persistent rain made it impossible for the finals to begin until late in the day when the doubles eventually got underway, but it lasted only five games before Germany's Dirk Dier limped off the court with a knee injury. Dier twisted his knee in the third game but after consulting a physiotherapist he played on for another two games before he succumbed to the pain and retired. He and compatriot Alexander Mronz were leading 3-2 when the former decided to stop, conceding a default to the American-Japanese combination of Tommy Ho and Shuzo Matsuoka. The skies opened again before the singles final between Mexican Oliver Fernandez and Sweden's David Engel could start and Ecuadorean tournament referee Fabricio Valdevieso decided to postpone the match when they were still unable to start at 8 pm. ''It's no use waiting any longer, we've checked the weather report and rain has been forecast for the rest of the evening,'' said a frustrated Valdevieso. The finals has been rescheduled for 9.30 am today. Engel, ranked 175th in the world, has reached two Challenger finals in Germany this year but his last tournament win was four years ago in Helsinki, Finland.