Edmund never looked like losing and had no trouble at all beating the 38-year-old Spaniard in straight sets, even with a tie-break being required in the second.
World number 69 Edmund has endured a very tough year, but he was again inspired playing for Britain as he gave Lopez the run around.
Rublev continues fine run with easy win over Lopez
The 24-year-old broke serve immediately in the opening set to assume a commanding lead and Lopez was never able to respond.
Lopez was drafted into the Spanish team at very short notice after Pablo Carreno Busta withdrew with a leg injury giving Edmund just five minutes to prepare.
"I was just enjoying going out to the semi-finals of a Davis Cup against Spain," said Edmund.
"I knew it was going to be loud out there. And it almost, in a way, it didn't matter who I was playing, I was just concentrating on being me first and putting myself out there.
"And I dealt with it really well, I thought."
Dan Evans will now take on world number one Rafael Nadal in the second rubber with a doubles decider expected later in the evening.
Edmund's losing run continues in Cologne
US Open men
Djokovic bounces back from losing first set to see off Edmund