Henman had not played since Wimbledon

Henman lost the first set on a tie-break but battled back to win 6-7 6-3 7-5 against rank outsider King, who is ranked 387 in the world.

Henman will play Janko Tipsarevic or Jan-Michael Gambill in the third round.

Five-times champion and fourth seed Andre Agassi lost in straight sets to Italian qualifier Andrea Stoppini.

The 36-year-old Agassi, making his 17th and final appearance at the Washington event, had no answer to Stoppini's strong serve and crisp groundstrokes, losing 6-4 6-3 in 62 minutes.

Agassi said: "I was very frustrated. I wanted really bad to get out there and be comfortable and hit my shots.

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"But I felt with every point the court got smaller and smaller. I had a harder time keeping the ball in the court. I never found my rhythm."

Stoppini, ranked 246th in the world, won his first career ATP match against Paul Goldstein on Monday.

Henman was satisfied with his win despite being taken to three sets.

"It was a really good test," Henman told his website.

"I was pleased with the way I played and even after dropping the first set I always felt I was playing well enough to win and there was nothing to panic about.

"I enjoy playing here. The heat is always a factor and I know a couple of guys pulled out yesterday but fortunately for me it wasn't a problem.