The Spaniard earned his first win over the Scot—who intends to retire after Wimbledon this year because of an ongoing hip problem but said he may not make it that far—in what was their fourth meeting as he won 6-4, 6-4, 6-7 (5), 6-7 (4), 6-2 after more than four hours on court in Melbourne.
Per the Guardian's Jacob Steinberg, Murray hinted he intends to continue playing:
"If this was the last match it was an amazing way to end. I gave literally everything I had.
"It wasn't enough tonight, so congratulations to Roberto and his team. I don't really have anything else to say. Thanks to everyone. My team, my family, everyone who helped me down the years.
"Maybe I'll see you again. I'll do everything possible to try. If I want to go again I need to have a big operation which there's no guarantee I'll come back from but I'll give it my best shot."
Having visibly struggled recently in practice with Novak Djokovic, Murray looked in better shape early on as he started well with a pair of comfortable holds, as Eleanor Crooks of the Press Association observed:
Bautista Agut looked to test him by moving him around the court as much as possible during the longer rallies, but the 31-year-old held his own admirably as a partisan crowd cheered him on.
Murray had the chance to take the eighth game when Bautista Agut sent a forehand slice into the net, but a netted backhand allowed the Spaniard to come back to deuce and hold.
The No. 22 seed punished Murray's failure to convert the break point in the following game as he drew first blood to take a 5-4 lead. From there, Bautista Agut quickly served out the set, the first time he had taken one off Murray.
Tennis writer Carole Bouchard summarised his performance early in the second set:
Indeed, he hit a fine winner down the line to earn two break points and the chance to take a 2-0 lead:
He was unable to take either, though, and soon after he was 3-2 down, having been broken himself as Bautista Agut began to turn the screw.
The second set soon followed, with Murray forcing his opponent to serve out the set but failing to otherwise trouble him, and Bautista Agut sealed it with an ace.
Murray's challenge looked to be over and done when he was broken to 15 early in the third, but even as his body fails him, the three-time Grand Slam winner showed he still has his trademark resilience when he grabbed a break back to the delight of the crowd:
Galvanised, Murray followed that up with a hold to love, and after producing a superb backhand winner down the line to save break point, he took a 5-4 lead. After surviving a set point, Bautista Agut was able to hold and the pair soon went to a tiebreaker.
Undeterred, Murray dug deep to take the match to four sets, doing so emphatically with an overhead smash.
He struggled to trouble Bautista Agut's serve in the fourth as he had in the third, but he continued to grind out holds of his own with remarkable tenacity and drag it to another tiebreaker.
Murray somehow found another gear in the tiebreaker, racing to a 6-1 lead to earn five set points. Bautista Agut regained some composure to save three, but he sent a forehand into the net to prompt a decisive fifth set.
Early in the fifth, five-time Australian Open finalist Murray won the rally of the match, and sports writer Tumaini Carayol could scarcely believe his eyes:
His efforts looked to have taken their toll, however, and Bautista Agut capitalised with back-to-back breaks of serve to take a commanding lead.
He stopped the rot at 5-1, saving a match point as he forced his opponent to serve it out. Bautista Agut did so to love, but it was Murray who earned the standing ovation from the crowd.
Bautista Agut will play John Millman in the second round, while Murray will be left to make a decision on his future after his remarkable exertions.