Britain's Andy Murray won a gruelling encounter against France's Gilles Simon to reach the quarter-finals at the Erste Bank Open in Vienna.
Murray, the top seed and world number two, won 4-6 6-2 6-2 and will face American John Isner in the last eight.
The Scot, 29, could be within sight of the world number one ranking if he wins the title in Austria on Sunday.
Another victory at next week's Paris Masters would mean Novak Djokovic must have made the semis to retain top spot.
Murray has now won his last 12 matches, taking in titles in Beijing and Shanghai as he tries to capitalise on a chance to finally top the rankings.