A shock looked on the cards early on as Giorgi, 26, produced some blistering tennis and stretched the giant Williams to win the first set 6-3 in this quarter-final match. She delivered three aces to the American's one in the first set and won 84 per cent of points on her first serve - with a consistent delivery of almost 120mph.
But 25th seed Williams fought back hard to level after taking the second 6-3, as the Italian was pushed back but the brute force of the American.
Williams, 36, crucially broke serve in the third game of the deciding set as she capitalised on some uncharacteristic errors from the tenacious Giorgi to win 6-4 and register her 19th consecutive victory at SW19 and reach the semi-finals for the 11th time.
But Giorgi, who enjoyed her best-ever run at Wimbledon, can take heart from her performance, with the promise of more to come.
Williams will face 13th seed Julia Gorges in Thursday's semi-finals.
