Nishikori played fantastic tennis in the opener, laying down the gauntlet to Murray. And while the world No. 1 was not at his fluid best, he battled back in the second and took a dramatic third in a tiebreak.
With Nishikori struggling on serve, Murray continued to turn the screw in the fourth set, and with his opponent despondent, he surged through the stanza to wrap up the contest.
Next up for Murray is a showdown with No. 3 seed Stanislas Wawrinka, who was imperious as he coasted past Marin Cilic 6-3, 6-3, 6-1 in his quarter-final on the same day.
Sometimes, even for a player of Murray's pedigree, there's not much that can be done when someone of Nishikori's class is at his best. And the Japanese was in that desirable groove to begin the match.
He secured an early break and smothered the top seed, taking shots early and leaving Murray swiping at thin air. Another break of serve gave the first set an emphatic 6-2 scoreline.
As Eleanor Crooks of the Press Association noted, it didn't take Nishikori long to wrap up the first stanza:
Murray was lacking his trademark spark until midway through the second set, as the Scot snatched the first break point available to him. From there, Nishikori lost the conviction that was so prevalent in his play early in the match.
The top seed went on to break his opponent again, and it felt as though the momentum shifted back in the Briton's favour.
Per former British No. 1 Annabel Croft, an altercation with the official lit a fire under Murray:
That changing dynamic seemed set to continue in the third as Murray broke first. Nishikori responded immediately, although the Scot stepped it up once again at 5-5, putting himself in a position to serve for the set.
Remarkably, Nishikori fought back again to force a tiebreak. The Japanese came apart at the end of the set, though, succumbing to a 7-0 loss. As you'd expect, the eighth seed was far from happy with his efforts, per Eurosport:
At the start of the fourth, Nishikori channelled that anger in the right way, producing some sublime touch to break. But once again, he struggled to build momentum, and a diligent Murray pegged him right back.
The Japanese was having issues on his serve at that juncture, and after a Murray hold, the world No. 1 piled the pressure on the Nishikori serve again. For the third time in succession, he was able to break, and the Scot had one foot in the semis.
It was clear Nishikori felt that was the case, too. Previously so vibrant at points in the match, he was trudging around court and looking to the skies. Murray, meanwhile, got on with the job, as another break took him to within one game of victory.
Unsurprisingly, the three-time Grand Slam winner seized the opportunity to set up a meeting with Wawrinka. Per the tournament's official Twitter feed, getting to the last four is a familiar feeling for Murray:
Getting past the Swiss will be a tough ask. Wawrinka has played superbly at Roland Garros this year, and given he usually improves as Grand Slam tournaments rumble on, there's no doubt he'll be Murray's toughest challenge yet.
Still, given there were major concerns about Murray's form ahead of this tournament, the top seed will be delighted with the steady improvements he's made at Roland Garros.