However, a rain delay before the second singles was the only thing that could slow Williams’ bid to get the tie back on level terms.
The reigning Wimbledon and US Open champion subdued Larsson in 66 minutes, extending her perfect record in Fed Cup singles to 9-0.
“I just try to fight and do the best I can,” said Williams, who blasted five aces and 31 winners and converted four of her five break chances. “I’m here for the team. Even though I don’t feel pressure, I’m here to give 100 percent. If I don’t feel 100 percent, I’m still going to try to give that.”
In yesterday’s reverse singles, Williams was to play Arvidsson and Stephens was to take on Larsson.
The fifth rubber was to be a doubles encounter with Arvidsson and Larsson teaming against the American tandem of Venus Williams and Varvara Lepchenko.
Serena and her former top-ranked sister Venus are playing Fed Cup together for the first time in 14 months.
The US team is trying to avoid relegation to World Group II after losing their first-round tie 3-2 to Italy in February.
A victory over Sweden would keep the Americans back in the World Group for next year.