Lopez and Verdasco defeated David Nalbandian and Agustin Calleri, 5-7, 7-5, 7-6 (5), 6-3, boosting Spain's hopes of winning the best-of-five championship on the road despite the absence of an ailing Rafael Nadal.
Spain could be in good position for its third Davis Cup crown if Argentina's leading player, Juan Martin del Potro, cannot play reverse singles today because of injury.
"This was an important victory; it gives us life," Spain captain Emilio Sanchez Vicario said. "We need one more game."
Today's schedule has del Potro meeting David Ferrer, then Nalbandian playing Lopez at Islas Malvinas Stadium. On Friday, Nalbandian defeated Ferrer in straight sets and del Potro fell to Lopez in four.
Spain has never won the Davis Cup away from home. Argentina, unbeaten at home since 1998, has to sweep both for its first Davis Cup triumph. But its hopes became bleaker Saturday, with Potro undergoing treatment on his right thigh after hurting it in Friday's singles. If he cannot play, he could be replaced by Calleri or Jose Acasuso.
Calleri and Nalbandian, playing their first Davis Cup doubles since the 2006 final, won the first set, but they couldn't hold back the veteran Spanish pair over 3 hours, 18 minutes.
The Spaniards had 86 winners and only 30 unforced errors. The Argentines struggled on serve and were broken six times. But they came through first, breaking Verdasco for 6-5. then erasing a 0-40 deficit for Nalbandian to hold and win the first set.
The rally pumped up the crowd, and the nearly 10,000 fans chanted constantly between games.
"These are very special matches, when you are playing for your country," Lopez said. "I didn't expect to win yesterday and didn't expect to win today, two consecutive matches like this."