By Simon Cambers
The win kept alive Belgium's hopes of qualifying for Saturday's final as winners of Group A, though they will have to beat top seeds Serbia in their remaining group match to stand a chance.
In just her second match since Wimbledon because of a serious elbow injury, Henin was still a little rusty but had too much experience and nous for world number 140 Karatantcheva.
Having only arrived in Perth late on Monday as a replacement for the injured Yaraoslava Shvedova, Karatantcheva did an admirable job and had Henin worried when she broke to lead 3-1 in the second set.
But the seven-times grand-slam champion regained her composure to reel off five straight games to clinch victory, before joining Bemelmans to win an entertaining doubles.
"It's not that easy especially after the injury so I am working hard to come back," Henin said.
"It's the first two matches so I know it's going to take a bit of time but it's just great to have the opportunity to play a few matches and have competition again."
World number 178 Bemelmans had pushed Lleyton Hewitt in his opening match and took his game up another level as he outplayed Golubev, ranked 142 places above him.
The 22-year-old looked nervous when he squandered three match points on the Golubev serve at 5-3 but held on to serve out for one of the best victories of his career.
"Though I lost my first match I stayed positive and it was great today," Bemelmans said. "I played very well and it's my best win in terms of ranking."
Top seeds Serbia were to take on hosts Australia in the day's other Group A match.
(Editing by John O'Brien)