Serena Williams was back in the Fed Cup on Saturday for the first time in five years, giving the United States a strong lineup.

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 Sunday with two more singles matches and one in doubles.

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 straight 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 Sunday, but it may 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 didn't seem at all bothered by the nagging ankle injury that hampered her during the Australian Open. She improved to 5-0 in Fed Cup singles.

She was cheered on courtside by older sister Venus, who is listed on the U.S. doubles team for Sunday 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.

As close as the sisters are, Serena said it may be difficult to focus solely on her upcoming match Saturday night.

"I'm going to try to relax," she said. "You know, have a team dinner, talk about our game plan, go from there. That's all we can do."

The winning team advances to a playoff round and a shot at the Fed Cup top tier, which the U.S. team was bounced from last year.

If Serena Williams can lock it up with a win in the opener, U.S. captain Mary Joe Fernandez could play Venus Williams in the second singles match instead of doubles. It may depend on whether Venus Williams would prefer to ease into her comeback teaming up as scheduled with Liezel Huber, the world's top-ranked doubles player.

Singles is also an option, but an unlikely one, if Belarus cuts the lead to 2-1 with a win in the first match.

"In the team competition, anything can happen," Fernandez said. "Even though we're up 2-love, there's a lot of work to be done still. We'll focus on that first one and go from there.

The Belarus lineup is going to depend on how Azarenka is feeling. She said her back has been bothering her since the Australian Open and the long flight to the United States didn't help.

Belarus captain Tatiana Poutchek said Azarenka's back was bothering her before the Australian Open, but it didn't show as she routed Maria Sharapova 6-3, 6-0 for her first Grand Slam title.

"She tried to warm up and she said she wouldn't be able," Poutchek said.

Poutchek said she'll see how Azarenka feels Sunday morning before deciding on the Belarus lineup.

McHale was 0-3 in Fed Cup play before her victory Saturday. She opened by winning the first 10 games, then survived a scare in the second set when Yakimova rallied from 4-0 to tie it.

Yakimova didn't appear ready early, but pushed the young American in the second set before McHale closed it out. She broke Yakimova, then held serve after falling behind love-30.

"I started to feel the nerves when I had the big lead in the second," McHale said. "But I was happy that even though I lost a couple of games there, I stayed focused and won those two games in the end."