A South African judge has convicted former Grand Slam doubles tennis champion Bob Hewitt of rape and sexual assault decades after the alleged assaults.

Judge Bert Bam said on Monday that he is satisfied that the two women who had accused the veteran tennis player of rape and a third woman who had accused him of sexual assault were telling the truth.

The charges stemmed from events in the 1980s and 1990s, when Hewitt coached the women as young girls. Hewitt, who is 75 years old, denied all three charges.

The judge said the striking similarities among the three victims' testimonies showed that Hewitt's conduct was calculated.

Bam ordered that Australian-born Hewitt should be taken into custody.