Each of the Japanese’s three Grand Slam semifinal appearances have come in New York and he exorcised some of the demons still lingering from his 2014 final heartbreak in Arthur Ashe Stadium by disposing of his attacker from that early September evening four years ago. Novak Djokovic or John Millman await in last four.
His astonishing record in deciding sets was only polished with the victory - earned despite squandering a break in the fifth set - but a place in the semifinals looked far-fetched when Cilic lead by a set and a break earlier in the afternoon.
Cilic had been forced to work harder during the previous four rounds, rallying from two sets down against Alex De Minaur in the third round, but he showed no signs of fatigue in an opening set that flashed by in 36 minutes.
Nishikori, as he is often guilty of, was struggling to find his rhythm, coughing up a break in the fourth game after a lengthy hold to open proceedings.
To make matter worse the Croatian dropped only four points behind his own deal, varying his serves to good effect and he broke Nishikori for the second time to seal the opening stanza.
The Japanese was staring down the barrel when Cilic broke for 4-2 in set two but it was that disappointment which sparked Nishikori into life. He restored parity with a break to love and, finally finding some length off his forehand wing, broke for the first time in the match and served it out after 42 minutes of ebbs and flows.
Breaks were traded in the third set, with Cilic crucially breaking back for 4-4, and a tie-break would be forced to separate the duo. Mini-breaks were aplenty - seven in total - and it was Nishikori’s mind games which tricked Cilic into surrendering the set.
Switch in momentum
Two inexplicable double-faults as the Japanese altered his return positions handed Nishikori the initiative and he produced a sumptuous backhand return winner down the line on set point to deepening Cilic’s misery.
The world number seven, who has reached two Grand Slam finals since his triumph in 2014, did steady the ship in the fourth set and his superiority told as he grabbed the all-important break in the seventh game to send the match into a decider.
Neither player is unfamiliar with the anxieties deciding sets conjure - they played a marathon five-setter in 2010 in New York - and it was Nishikori who struck the first blood as he broke for 3-1.
And when he consolidated for 4-1 the match seemed as if it was heading in only one direction, especially as he carved out a break point opportunity for a double break of serve.
That, however, spurred Cilic into action, as he fended off the world number 19’s advances and broke back to even the scales.
Both players held their own deals but it was Cilic who blinked first, relinquishing two match points. It then only seemed fitting that Nishikori sealed his place in the semifinals with a return winner.