But with the two best runners-up from the six groups earning a spot in the quarter-finals based on the number of ties, sets and games won, the walkover could work in U.S. team's favour.
'That was our bad, ' said Murray.
Canada kicked off the newly revamped Davis Cup competition in blistering fashion on Tuesday, as Vasek Pospisil beat Reilly Opelka and Denis Shapovalov defeated Taylor Fritz to give the Canadians their first-ever success over the USA in 16 Davis Cup attempts. Canada has lost both doubles matches, with Shapovalov and Pospisil falling in three sets to Italy on Monday.
However, an increasing number of top players have skipped matches in recent years to ease their schedule.
The revamped tournament is the result of a 25-year partnership between the International Tennis Federation and Kosmos, a group co-founded by Barcelona soccer player Gerard Piqué.
"The ambiance changed into unheard of", said Nadal.
Khachanov stretched him to breaking point at times, especially in the second set, but the 19-times Grand Slam champion fought off a set point before claiming victory.
Should the US beat Italy later, the 6-0 6-0 doubles win they were "gifted" by Canada could potentially help them as one of the two best runners-up who will join the six group winners in the quarter-finals.
"I respect that (Pique) is trying to do something new and different in tennis", Murray told reporters.
For Murray, the Davis Cup is a chance to continue his remarkable comeback from injury while also returning to team tennis, a format he has always enjoyed.
"I think that was one of the things that some of the players were anxious about playing at a neutral venue but I thought the atmosphere was brilliant from both sets of fans".
Kazakhstan, who will face Andy Murray and Superior Britain in Community E on Wednesday, wished Mikhail Kukushkin and Alexander Bublik to make a selection the doubles rubber 6-4, 7-6 (7/2) in opposition to Dutch pair Robin Haase and Jean-Julien Rojer. The squad arrived at Madrid's Barajas airport on Wednesday.
But holding either tournament after the US Open will prove hard given that week already carries the Laver Cup, the competition promoted by Roger Federer´s management company Team8, contested between Europe and a Rest of the World team.
Murray had only ever lost three singles matches before in the Davis Cup and responded by breaking Griekspoor at the start of the second set.
Murray, the two-time Olympic champion in singles and a three-time Grand Slam victor, has been slowly coming back to full speed after undergoing hip surgery in January.
German world number seven Alexander Zverev was clear from the outset that he would not compete and has instead made a decision to play in an exhibition match against Federer - whose management company he is signed to - in Mexico.
From Andy Murray there was the unprecedented confession that he had let his high standards slip when it came to preparing for this Davis Cup finals week. The only negative thing in my opinion is we are just starting the last match at 1 a.m.
"Playing at one week, at one venue, deciding it all, is not the Davis Cup".
Seven of the nine sets in singles matches went to tiebreaks, with Canada winning six of them.
How does the ATP Cup affect the Davis Cup? The Russian national team won the prestigious competition twice in 2002 and 2006.
"It feels like there's a few people that want to bash the event before it's started".
The 32-year-old Djokovic said he expects "fun" games in Japan.
"I personal to protest, it's a habitual feeling", said Mahut. "I think that this is the logical step for the future".