A stuttering Roger Federer and a rampaging Rafael Nadal need to clear only one more hurdle before setting up a tantalising final showdown at the Qatar Open.
Federer appeared to have left his A game behind in the locker room on Thursday as he dropped his first set this week before eventually taming Italy's Andreas Seppi 6-3, 5-7, 6-4.
While the Swiss, who won the last of his record 16 Grand Slam titles at the Australian Open two years ago, extended his winning run to 20 matches, Nadal shunted aside Russia's Mikhail Youzhny 6-4, 6-4.
Hoping to block the much-anticipated Federer-Nadal final will be a pair of entertaining French showmen.
Jo-Wilfried Tsonga booked a semi-final date with Federer in Doha for the second year running after rolling over Spain's Albert Ramos 6-2, 6-1.
Monfils made sure that the top four seeds all lived up to their billings with a 6-2, 6-3 win over Serbia's Viktor Troicki.
Defending champion Federer played Tsonga eight times in 2011. Although the Swiss came out on top on six occasions, he is unlikely to underestimate Tsonga's credentials especially since the Frenchman beat him at his beloved Wimbledon last June.
"Both of us struggled getting to the semis," Federer told reporters. "I struggled today. He struggled in the first two rounds. But I think when we play each other, it's more straightforward because we know what to expect. There are no more secrets."
Tsonga will go into the semi-final in good heart following a dominant performance against Ramos. The world number six was untroubled on serve and increasingly expansive as he wore down the fading Spaniard, advancing to the net to hit a range of backhand, forehand and smash winners.
"It's difficult to play against him (Federer)," Tsonga said. "I have to be perfect and play my best tennis. I know I can do it."
Nadal's battle with Youzhny was arguably the match of the tournament.
After squandering two break points in the opening game against Youzhny, Nadal made no mistake on his next opportunity a couple of games later. He dragged Youzhny into a gruelling rally and pumped his fists in delight as the tiring Russian slugged a backhand into the net.
In the second set, the Russian seventh seed was left frustrated as he failed to convert a string of break points. He allowed Nadal to gallop into a 4-1 lead as the Spaniard peppered the court with a series of sliced backhand and searing forehand winners.
Former top 10 player Youzhny clawed back one of the breaks after following up a delightful dropshot winner with a powerful forehand drive, which closed the gap to 4-5.
However, Nadal would not be denied and clinched victory with a volley winner.
"I think I played my best match here today," Nadal said. "It's one of the days I go back to the hotel very, very happy about what I did. For a lot of moments, I played at very, very high level, moving very well, going inside the court, having the control of the point."
Monfils prepared for his battle with Nadal by winning 15 of the last 20 points against Troicki.
Despite beating the 10-times Grand Slam champion only once in nine meetings, he remains unfazed.
"Statistics change," Monfils summed up.
