The British No 1, who had failed to win a match in his first two tournaments of this year's American hard court season, appears to be rediscovering his top form with the US Open a little more than a fortnight away.
Henman, instead of trying to serve and volley, worked his way to the net at every opportunity and ultimately clinched the opening set with a lob which Kiefer smashed into the net.
The Briton then attacked Kiefer's serve throughout the second set and breaks in the fourth and sixth games were enough to bring him his second success in four attempts against the German, earning him a meeting with the fourth seed, Yevgeny Kafelnikov of Russia.
Henman's win means he now has the opportunity to intervene in the battle for the world No 1 ranking. Kafelnikov, who beat Sweden's Jonas Bjorkman, 6-1, 6-4, can regain the top position from Pete Sampras, who yesterday celebrated his 28th birthday with a 7-5, 7-6 victory over Germany's Rainer Schuttler.
The tournament director, Paul Flory gave Sampras, a birthday cake after the match. The way Sampras has been playing the past month, Flory could be giving him the winner's cheque for the third time on Sunday.
"I felt pretty good, even though I got off to a tough start," Sampras said. "I raised my level when I had to. I think he was feeling the pressure a little bit. I knew eventually I was going to come around. There was no reason to panic."
The victory extended Sampras' streak to 19 matches, during which he has won three tournaments. But as a measure of the way Sampras has dominated men's tennis - finishing No 1 for a record six straight years - the 19 wins only tied the third-best streak of Sampras' career.
Sampras failed to hold his serve in the fifth game yesterday. But, with Schuttler serving at 5-4, Sampras gave the 23-year-old German a clinic, winning 12 of the next 15 points. He broke Schuttler twice with a variety of down-the-line and crosscourt shots, and shocked him with a 134 mph serve. Sampras thoroughly controlled the second set tie-break, unleashing two 130-mph-plus serves.
Pat Rafter ignored hot air balloons, a light aircraft and a flight of geese on Wednesday night to pound out a 7-6, 6-3 win over Daniel Vacek.
Rafter, who won this title last year before going on to win his second successive US Open championship, remained focused against the Czech player despite the interruptions from the air. At one point in the first set it appeared that an invasion from the skies was imminent as two balloons took off on the tournament grounds and flew over the stadium. Seconds later a small plane all but "buzzed" the stadium.
Yesterday Rafter made further progress by beating the 15th seed, Nicholas Lapentti of Ecuador, in straight sets.
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