The United States defeated Belarus 5-0 in their Fed Cup World Group-II tie at Worcester, Massachusetts, on Sunday.
Serena Williams rallied from a set down to beat Anastasia Yakimova 5-7, 6-1, 6-1 in the day's first singles match to give the Americans an unassailable 3-0 lead.
Her elder sister Venus, playing her first official match since last August, teamed with Liezel Huber for a 6-1, 6-2 doubles victory over Yakimova and Daria Kustova for the final US point, after Christina McHale beat Kustova 6-0, 6-1 in the meaningless fourth singles.
Venus is a seven-time Grand Slam champion, but had not played since pulling out of the US Open, when she announced she had been diagnosed with the auto-immune disorder Sjogren Syndrome.
Serena, a 13-time Grand Slam champion, had opened her weekend with a victory over Olga Govortsova on Saturday, when McHale beat Yakimova.
Yakimova was a late replacement for Australian Open champion Victoria Azarenka, whose triumph in Melbourne saw her claim the women's world number one ranking.
Azarenka had been expected to lead Belarus but pulled out with a sore lower back. She said travel from Australia had exacerbated the problem.
The United States advanced to a World Group Playoff and will now play for a chance to return to the elite group in 2013.
The United States have won the women's nations competition a record 17 times and are playing in the World Group-II for the first time.
Belarus have never played in the World Group.