Lopez, 37, was contesting the tournament's singles final before pairing with Andy Murray in the doubles final later in the afternoon.
It was a relatively straightforward first set for the Spaniard, who broke Simon's serve in the very first game before securing another break soon after to lead 4-1. While Simon, 34, earned four break points during the opening set, the Frenchman failed to convert any of them, and Lopez ultimately took the set 6-2.
Simon was at last able to demonstrate some composure at the start of the second set, gaining an early break to lead 2-0, but Lopez quickly returned the favour to restore parity. There was little drama throughout the remainder of the set as neither man faced another break point, meaning a tiebreak was required to separate the players.
It was Simon who was able to hold his nerve in the back-and-forth breaker, sealing the hour-long set 7-6 (4) and forcing a decider.
There was no shortage of break points on either side of the net early in the final set, but the players eventually settled down with a series of comfortable holds. Tension returned in the 12th game of the set, however, as Simon struggled to hold serve, saving one match point before finally surviving to set up another tiebreak.
Spain's Lopez -- ranked 113th in the world as a singles player -- surged ahead in the breaker, earning four match points and converting the second to lift this first trophy of the season.