Olympic bronze medallist Wang Zhen had looked set to claim the host country's first gold medal in Beijing after bursting clear at the 13km mark, only for the European champion to relentlessly reel him in over the last five kilometres.
Lopez, who took bronze in Moscow two years ago, turned on the power over the last two kilometres as his rivals wilted in the fierce morning heat, clocking a winning time of one hour, 19 minutes and 14 seconds, a personal best.
Wang was met with a huge roar at Bird's Nest stadium as he crossed the line to take silver in 1:19:29 while Canada's Benjamin Thorne took bronze in 1:19:57.