Henman, the No 1 seed, who turned down the chance to play in the lucrative Grand Slam Cup in his search for ATP points, beat the 28-year-old Frenchman, who was playing his first tour match of the year, 6-1, 6-2.
Guardiola faced a succession of powerful serves and fierce forehand returns from the British No 2, who now plays another Frenchman - Stephane Huet or Nicolas Escude.
Henman is battling to recover his form after a poor run on the US hard- court circuit, during which he was eliminated in the first round of the US Open by Guillermo Canas, and lost to players ranked outside the top 50, including Guillaume Raoux and Jan Kroslak.
"Prior to the Davis Cup I was playing badly. My game was better there, and I want to build on that," Henman said. "This win is another step in getting my confidence back."
Henman's aim is now to qualify for the ATP World Championship in Hanover in November. "I am in 11th place, so I need some points. But after a disappointing summer I am not looking too far ahead," he said.
The No 7 seed, Fabrice Santoro, one of the heroes of France's Davis Cup semi-final win at the weekend, fought back from the brink of defeat to beat the 85th-ranked John Van Lottum 4-6, 7-5, 6-0.
The temperamental Dutchman served for the match at 5-4 in the second set, but his game collapsed as Santoro reeled off the next nine games.
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