American Mardy Fish and Bulgaria's Grigor Dimitrov had to be separated by the match referee when they squared up to each other during a changeover in a bad-tempered Hopman Cup encounter on Friday.
The pair traded insults throughout their singles match and the mixed doubles before the tie between the two bottom teams in Group A ended with a 2-1 win for Bulgaria over the defending champions.
Dimitrov, in a hurry to get through the tie as he had to catch a late-evening plane to Sydney, thrashed World No. 8 Fish 6-2, 6-1 in the singles before helping Tsvetana Pironkova to beat the American and team-mate Bethanie Mattek-Sands in the mixed doubles.
Fish, who also lost in straight sets to Czech Tomas Berdych on Wednesday, directed angry words at Dimitrov while the pair were shaking hands after the singles at Burswood Dome.
During the doubles, Fish appeared to hit a ball straight at the Bulgarian and then approached him as he sat in a chair during a change of ends.
Dimitrov jumped to his feet and the two men argued fiercely before the match referee rushed on to the court and stood between them. It was nearly a minute before order was restored.
"What can I say? It was one of these days when every touch goes in," said Dimitrov, the World No. 76 and a former junior champion at Wimbledon and the US Open.
"Mardy was not on top of his game, but I think we had great rallies and gave a bit of entertainment as well. It's nice to have a win like this under my belt. I'm playing against a top-10 player and I've beaten him. Whatever I touched, it went in."
Mattek-Sands defeated Tsvetana Pironkova 6-4, 6-4 in the opening match and Bulgaria had an 8-5 win in the mixed which was reduced to a single pro set so that Dimitrov could catch his flight.
Dimitrov and Pironkova took to the court for the doubles at 2110 local time, knowing that Dimitrov had to be on a 2350 flight so that he could play in qualifying for the Sydney International on Saturday.
He was rushed to the airport after the doubles finished at 2220.
Group winners the Czech Republic and France had already qualified for Saturday's Hopman Cup final.