By Greg Stutchbury
Former world number one Henin, who returned to competitive tennis at the Brisbane International after an 18-month retirement, beat her fellow Belgian Kirsten Flipkens 6-4 6-3.
"I think it was a very difficult day for all of us," Dementieva told reporters. "Ten hours waiting to come on court was quite difficult. I'm just glad that we were able to finish our match today."
The 28-year-old Dementieva never allowed Dushevina to settle, clinically dismantling her service game with constant pressure which yielded six breaks.
Dementieva said she had not seen Henin's match but knew the Belgian would be a difficult opponent despite her rustiness.
"I think it's going to be a tough challenge because Justine, she's a very experienced player," she said.
"I'm sure she was getting ready for this comeback. So I'm just expecting a tough match against her."
(Editing by Ed Osmond)