Tampa's Mardy Fish defeated Alejandro Falla 4-6, 6-1, 6-4, 3-6, 6-4 on Friday to give the United States a 1-0 lead in its Davis Cup match against Colombia.
Colombia's Santiago Giraldo beat Sam Querrey 6-2, 6-4, 7-5 in the day's second singles match.
After a doubles match Saturday, the competition at on red clay at La Santamaria bullring - about 8,700 feet above sea level - will conclude Sunday with reverse singles.
The winner Sunday will get a spot in the World Group. The United States, a record 32-time champion in the event, has dropped out of the World Group only once since it began in 1981.
"We've been in this situation before a few times - in a relegation match at 1-1 going into doubles," said U.S. captain Patrick McEnroe, retiring after the competition. "I feel good about our doubles. We have three players who have played together so there are a lot of options. I like that we have three or four players available (Saturday) and Sunday."
Ryan Harrison and Tampa's John Isner are set to play doubles for the United States, although Fish said he would be ready to step in. Colombia is expected to counter with Robert Farah and Carlos Salamanca.
In the World Group semifinals, France took a 2-0 lead over Argentina, and the Czech Republic and Serbia split their opening matches.
In Lyon, France, Michael Llodra beat Juan Monaco 7-5, 4-6, 7-5, 6-3, and Gael Monfils had 27 aces in a 6-4, 2-6, 6-4, 6-3 victory over David Nalbandian.
In Belgrade, Serbia's Janko Tipsarevic beat Tomas Berdych 7-5, 6-2, 2-6, 7-6 (5) to square the match after Radek Stepanek topped Viktor Troicki - playing after second-ranked Novak Djokovic withdrew - 4-6, 6-2, 6-4, 6-4 in the opener. Djokovic said he was tired after his run to the U.S. Open final.
Giraldo broke Querrey in the third set to take a 6-5 lead, then served out to pull Colombia even.
"I wasn't surprised how well he (Giraldo) played," Querrey said. "I have seen him play before and he hits the ball low and flat which is perfect for these conditions. It is difficult to adjust to the altitude."
The first match lasted 3 hours, 59 minutes, with Fish breaking Falla in the final game of the fifth set.
The home crowd of about 8,000 supported Falla with loud cheers.
"The key was staying ahead in the fifth set," Fish said. "I had some tough games to hold but was always able to stay ahead. When he had to serve to stay into it at 5-4, that's when all the pressure kicked in."
Fish has put more emphasis on fitness recently and it paid off with his fourth victory in five tries this season in five-set matches.
"I was a gutsy mental effort by Mardy today," McEnroe said. "It goes to show what being fit means."
Fish suggested both players might have an easier time on another surface.
"He (Falla) hits the ball flat and I think he would have preferred a hard court," Fish said. "We both would have preferred to play on a hard court. Maybe the tennis would be a little bit better."
The statistical categories were nearly even for the two, though Fish had a clear edge in aces - 8-1.
The Americans also may have the edge in history. The United States is 178-17 when winning the first match in a Davis Cup tie.
"The first set of both matches was pretty rough for us," McEnroe said. "We practiced well all week, but you can't simulate match conditions. Moving forward I think we're in good shape now that the guys have gotten a match under their belts at the altitude."