Serena Williams had to overcome a stubborn effort from Madison Keys to win the first all-American women's tour final for four years in straight sets and lift the Italian Open title in Rome on Sunday.

The world's best player demonstrated her readiness to begin the defence of her French Open title next weekend with a 7-6(5) 6-3 win but was so impressed with her 21-year-old compatriot that she predicted Keys could become a future world number one.

It was Williams's fourth title triumph in Rome in 14 years, her 70th career title in all and her first since winning in Cincinnati nine months ago.

The 34-year-old great has looked more vulnerable of late, losing in the semi-finals at last year's U.S. Open and final at the Australian Open and Indian Wells this season.

Yet even though this was her first claycourt appearance of the season, it was enough to confirm she is in fine shape for Roland Garros, with plenty of room also for improvement.

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