BRINDISI, Italy - Top-ranked Serena Williams overcame a stiff challenge in the opening set for a 7-6 (5), 6-2 win over Italy's Camila Giorgi on Saturday in a Fed Cup World Group playoff.

Italy's Sara Errani then evened the best-of-five series with the United States at 1-1 by routing 57th-ranked Lauren Davis 6-1, 6-2.

Neither player broke serve in a highly competitive first set in the opening match, which was only decided when Giorgi's forehand clipped the top of the net on Williams' first set point.

"The first set was tough," Williams said. "I just needed to stay calm and try to make more shots and try to hit deeper shots. I was hitting it a little bit short. Once I was able to hit deeper I was able to work it out."

Williams improved to 19-0 this year and 15-0 for her career in Fed Cup. The only blemish on Williams' record this year came when she withdrew before the Indian Wells semifinals last month with a knee injury.

Giorgi was a surprise choice by captain Corrado Barazzutti for Italy's second singles spot over Brindisi-born Flavia Pennetta but the 23-year-old showed surprising poise and was even able to match Williams' power in the opening set.

Giorgi matched Williams with 17 winners apiece in the first set — which lasted more than an hour — while Williams committed 18 unforced errors to Giorgi's 15.

Unable to impose her game, Williams appeared frustrated and kept shouting "Come on!" to herself in angrier and angrier tones as the first set wore on. And she consistently applauded, putting one hand to her racket, when Giorgi blasted winners by her.

But Williams played solidly in the tiebreaker and Giorgi missed two straight forehands to hand Williams the set.

"My game is very instinctive and I made two key errors," Giorgi said. "Two errors are not many but it depends when you commit them. In a tiebreak, two points are worth gold. But I have no regrets for how I played."

Williams took control early in the second set.

"I competed well," Williams said. "She played very, very well and I stayed in there. I didn't get negative. I stayed positive and just did the best that I could. I've been working really hard my whole life, so maybe it was just experience. I don't know."

The winner returns to the World Group and can compete for the Fed Cup trophy next year while the loser will be relegated to the World Group II.

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Andrew Dampf can be followed at www.twitter.com/asdampf