Serena and Venus Williams each won in straight sets to give the United States a 2-0 lead over depleted Belgium in their Fed Cup first round tie.
Five-time Grand Slam champion Venus Williams opened with a 7-5 6-2 triumph over Kirsten Flipkens while reigning Australian Open champion Serena Williams, a seven-time Grand Slam winner, defeated Caroline Maes 6-1 6-4.
The triumphs put the US on the brink of advancing to July's semi-final tie against either Russia or Spain.
Belgium, playing without either world No 1 Justine Henin or No 4 Kim Clijsters, would need an unlikely sweep of today's reverse singles matches as well as a doubles triumph to advance.
Venus Williams needed only 69 minutes to post a victory. She hit 34 of 56 first serves and lost only seven points when connecting on her first serve.
However, she did trail 5-3 in the first set before winning four straight games.
As the American stepped up the attack, Flipkens crumbled, double faulting on two key points.
"It was very windy and I rushed a few shots in that first set," said Venus, who double-faulted herself three times in the set. "There were a few serves there where at the last minute the wind takes the ball.