Simon continued his impressive form with a 6-4 6-4 demolition of Tipsarevic.
The Frenchman managed a break in each set, but it might have been even more clinical had Tipsarevic not saved eight of the 10 break points he faced on serve.
"It was a very, very good match today and I couldn't have done better than that," said Simon.
"Janko has been playing amazing tennis since last year; he is hitting hard and isn't losing a lot. I think I played the perfect match, but it will still close. It gives me confidence for the final."
Second seed Gasquet came within two points of defeat against Nieminen, but recovered to win 3-6 7-5 6-2 in just under two hours.
"It's tough to say how I turned it around," said Gasquet. "I tried to fight. I was playing badly and was frustrated after the first set. He wasn't missing. At 0-4 [in the second set], I served well on the big points and he got tense. He double-faulted at 5-4, which was the key of the match, and in the third set I played better."