Top-ranked Victoria Azarenka was hoping to provide a similar lift for Belarus, but she was sidelined by a lower back injury.
The Americans capitalized with straight-set victories by Williams and Christina McHale for a 2-0 lead in the best-of-five series, which concludes today.
McHale beat Anastasiya Yakimova 6-0, 6-4 before Williams overpowered Olga Govortsova 7-5, 6-0 in her first Fed Cup match since 2007, leaving the U.S. team just one victory away from advancing in the World Group II series.
Williams was inconsistent in the first set, winning the first three games before sputtering midway through as Govortsova tied it by winning three consecutive games.
Williams and Govortsova were tied at 5 before the American star won the last eight games of the match.
“I relaxed a little bit and started making more shots,” Williams said. “I thought she played excellent in the first set. She played pretty well in the second set, but I didn’t make as many errors.”
Williams is scheduled to play Azarenka in the opening match today, but it might not happen because of the back injury that forced the Australian Open champion to withdraw earlier Saturday.
If Azarenka can go, the day could open with a thriller. If not, whoever steps in for Belarus could be in for tough duty.
Williams was cheered on courtside by older sister Venus, who is listed on the U.S. doubles team for today in what would be her first match since the opening round of the U.S. Open in August.
Venus Williams has been battling an autoimmune disease that can cause fatigue and joint pain, but hopes to return to competition this weekend.