Henman had lost both of his previous matches, in Montreal last week and Los Angeles the week before, but he overcame the world No 93 as a result of some clever variations of pace.
Rain interrupted the day's play and Henman had to spend much of the evening waiting to go on court. He finally secured victory just before midnight.
After dropping his opening service game, he broke back immediately and when he broke again for 4-2 van Lottum angrily smashed the ball into the net. His game gathered pace in the second set in which Henman scored two more breaks in the fourth and sixth games.
"I tried to vary it as much as possible. It was a bit of a relief to win after losing in the past two weeks," said Henman. "I've got no complaints about the way I played tonight and now I feel much more ready."
Henman's next opponent will be either Nicolas Kiefer, the 10th-seeded German, or Paul Goldstein, the American who upset Greg Rusedski at this year's Australian Open.
Pete Sampras was made to work hard by Jan Siemerink of the Netherlands, in his second-round match, winning 7-6, 6-4.
The Wimbledon champion and world No 1 has received a birthday present from Queen's club in London. Sampras, who celebrates his 28th birthday today, has been granted membership of the club following his victories in 1995 and 1999 at both the Stella Artois tournament and at Wimbledon. John McEnroe, Jimmy Connors and Boris Becker are the only other players to have won both tournaments in the same year.
Serena Williams, playing in her first tournament since losing in the third round of the French Open in May, beat Elena Likhovtseva of Russia, 4-6, 6-3, 6-1, at the Acura Classic in Manhattan Beach, California.
Williams, the No 6 seed, is pleased to be back. "It was a little tough because I haven't played since the French Open," she said. "It feels good to be out there, playing and competing and trying to do well. I missed that," she said.
Anke Huber, of Germany, beat Wimbledon semi-finalist Alexandra Stevenson 6-4, 6-4.
Stevenson has had a memorable couple of months since turning professional this summer. She managed to become the first qualifier to reach the semi- finals of Wimbledon, then collected a bronze medal in the recent Pan-American Games. However, as a wild card entry, she failed to survive against Huber, the world No 24, who needed a service break in each set to win.
"I'm disappointed because I wanted to win this match but there's always next week," said Stevenson, ranked 41 in the world. "I think I played OK but I'm still learning."
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