Federer was clearly delighted with the manner of his win
World number one Roger Federer will take on Novak Djokovic in the last four of the Monte Carlo Masters after beating David Nalbandian 5-7 6-2 6-2.
Nalbandian, who had won his last two meetings with Federer, edged the first set without facing a break point.
But Federer hit back, reeling off four straight games to level the match before booking a semi against Djokovic.
Rafael Nadal will face Nikolay Davydenko in the other semi after beating fellow Spaniard David Ferrer.
Nadal, the world number two, had to recover from a break down in the second set before advancing 6-1 7-5.
Today I think it came together
Djokovic needed seven chances to finally break Sam Querrey's serve in the first set, with the American's drop shot hitting the net to give Djokovic a 5-4 lead and an opportunity to serve out the set.
The Serb converted all three breakpoint chances in the second and claimed the 6-4 6-0
victory on his third match point with a big forehand that bounced on the baseline.
Davydenko was the first man to book his place in the semi-finals with a 6-3 4-6 7-5 win over Russian compatriot Igor Andreev.
Federer, who is working with coach Jose Higueras in the build-up to the French Open, is now unbeaten in eight matches on clay.
However, this was by far his most impressive performance.
He lost a tight opening set after 52 minutes, sending a backhand pass wide at the crucial moment.
But after letting a 2-0 lead slip, he regained composure in the second set, winning four games in a row with some outstanding shots, including a stunning drop shot on the run.
He broke again in the sixth game of the decider with a service return into Nalbandian's feet and the Argentine could not recover.
"Today I think it came together and I was just happy the way I moved especially because on clay that is a big thing for me," said Federer.
"I could have served maybe a little bit better here or there. But my statistics, I think, were very good. So it's always nice playing against David, but also beating him."
Federer, who suffered from glandular fever earlier in the season, is experiencing his worst start to a season since 2004.
"It feels very good to be back like this, especially after my illness", he added.