Cross had the first throw, but both players began cautiously. The early tone was set by missed doubles, Cross passing up chances at double 18, and Littler narrowly missing tops for a 115 checkout.
The breakthrough came when Littler punished Cross's wobble on the outer ring, pinning tops to break before consolidating amid repeated double trouble from both players. Despite leaving 170 and then 164 in successive legs, Littler stayed composed and wrapped up the set with a tops finish from 70, averaging close to 100 while Cross lagged behind.
This was the first real swing in the contest. Cross found his range, landing his opening maximum and producing a clinical 109 checkout on double 16 to break throw. Littler's scoring dipped into trebleless territory for the first time in the match, and although he responded with a maximum of his own, Cross kept his nerve on double 10 to move 2-0 ahead.
Reigning champion Littler clawed a leg back via a 65 finish, but Cross held firm in the decider, taking out 32 after both players missed key doubles to hand Littler his first dropped set of the tournament.
Despite some irritation at stray darts into treble five, Littler's scoring exploded in set three. A 180 left him on 86 against the throw and, after Cross missed a bullseye on 90, Littler pinned double seven to steal the leg. Back-to-back maximums followed, setting up an 11-darter, before he produced one of the finishes of the night, taking out 128 via treble 20 and bullseye. Littler averaged around 125 in the set and surged back ahead at 2-1.
In the fourth, Cross had darts at 130 but missed double five, Littler failed on double 10, and both flirted with letting the set slip away before Littler finally held. Cross levelled cleanly on double 16, but Littler's confidence was now unmistakable.
An 11-darter via treble 19 and double 12 put him back in front, and although he narrowly missed the bull for a 121 checkout, Cross again faltered on the outer ring. Littler punished ruthlessly, pinning double 10 to break and take a 3-1 lead in sets.
But in true style, Voltage refused to fold. Under pressure, he held on double eight, then weathered Littler's relentless scoring to edge ahead.
Littler missed a chance at 161, and Cross responded with a stunning 126 checkout via treble 19, 19 and bullseye to snatch the set and drag the match into a sixth. Momentum had shifted once more, and the contest suddenly felt wide open.
What followed was a shoot-out of extraordinary quality. Both players averaged just shy of 120, trading maximums and heavy visits. Cross threatened a huge 167 checkout early on, only for Littler to calmly hold on double 12. When Cross missed tops from 82 for a break that would have levelled the match, Littler pounced, pinning tops for a decisive break.
From there, he did not look back. Another 180 left him cruising, and a precise 68 checkout via 16, 12 and tops sealed victory, Littler roaring in celebration as he booked his place in the last eight.
Littler finished with a 106.58 average, an astonishing 17 maximums and a 43 per cent success rate on the doubles. Cross, who averaged 98.92, can perhaps take some solace that he forced the defending champion to work harder than at any point so far in this tournament.
Luke Woodhouse or Krzysztof Ratajski await Littler in the quarter-finals.
Searle's career-best run
Ryan Searle powered into the World Championship quarter-finals for the first time in his career with a ruthless 4-0 demolition of James Hurrell to kick off the round four fixtures.
The opening set was competitive, with both players trading solid scoring and hovering around the ton mark. Hurrell landed timely maximums but failed to convert pressure into control, missing chances when presented with a look at 136.
Searle, unfazed, recovered from missed darts at tops to pin double five in the deciding leg and edge the set, setting an ominous tone.
Hurrell's doubling began to unravel in set two, and Searle moved in with clinical precision. A break of throw opened the set, followed by a tidy 18, double 20 finish to consolidate.
The defining moment came when Searle calmly dismantled 109 via treble 19, 12 and tops, sealing the set 3-0 while averaging 104.86. Hurrell left the stage shaking his head, already chasing.
Momentum stayed firmly with Searle in the third. He raced to five straight legs before Hurrell finally stopped the slide with an 80 checkout, though even that came after a stumble in the oche.
Hurrell's confidence on the doubles never recovered. Misses at tops and double 18 repeatedly invited Searle back in, and although Heavy Metal himself wobbled on a 138 attempt, he eventually pinned double 5 to close the set.
Hurrell's doubling percentage by this point had collapsed into the low teens.
Searle broke early in the fourth set, absorbing a brief Hurrell response before continuing to pile on pressure with heavy scoring. A 171 underlined his dominance and, although he missed the first dart at 94, he returned calmly to clean up on double four.
A 56 checkout moved him to the brink and, after Hurrell briefly halted the procession with double 19, Searle finished the job on tops to seal the match and a landmark quarter-final berth.
Searle finished with an average just over 100, an extraordinary 20 scores of 140 (yet just two maximums), and a 50 per cent success rate on the doubles. Hurrell, by contrast, endured a brutal collapse on the outer ring, converting just 18 per cent of his attempts and never recovering once the pressure mounted.
Either Jonny Clayton or Andreas Harrysson awaits Searle in the quarter-finals.
Rock routs Rydz
Josh Rock produced a composed, increasingly authoritative performance to defeat Callan Rydz 4-1 and book his place in the fourth round of the PDC World Darts Championship, recovering from an edgy opening set before overwhelming his opponent with sustained scoring power and superior finishing.
Rydz struck first in a nervy, emotionally charged opening set, capitalising on Rock's early missed chances. Rock twice threatened ton-plus finishes, including a visit that left 158, but missed double one to open the door.
Rydz pinched the opening leg on double 10, escaped again from 78 when Rock failed to punish on tops from 71, and although Rock briefly found rhythm with a maximum and a 105 to tidy up 60, Rydz closed the set with a pair of 140s and double eight.
Rock responded with authority. After Rydz held comfortably to start, the Northern Irishman lifted his tempo sharply.
A seven-dart burst set up an 11-dart leg, and although Rydz produced a sensational 10-darter from 141 in the decider, Rock refused to blink.
Breaking throw with 16, double 16, he levelled the match at one set apiece, his average climbing rapidly from the mid-80s into three figures.
Rock opened set three with his eighth maximum to leave 36 after nine darts and, despite missed chances, was repeatedly first to the finish.
A bullseye checkout for 86 underlined his growing confidence, and he wrapped up the set in 15 darts while averaging just shy of 110. Rydz was still competing, but the balance of power had shifted.
Rydz briefly halted the momentum in the fourth set, holding early to stop a run of four legs without reply. Errors crept in on both sides as the tension rose, but Rock again proved sharper in the key moments.
An 83 checkout clinched the set after a scrappy sequence of legs, extending his lead to 3-1 and leaving Rydz needing something special.
Rock raced away on his own throw in the fifth set, continuing to pepper treble 20 and landing another maximum to underline the gap in scoring.
Rydz kept himself alive with a fine 110 checkout, but the respite was short-lived. Throwing for the match, Rock rolled in another 180 and then sealed the contest in style, taking out 112 with treble 20, single 20 and double 16.
Rock finished with a 98.98 match average, nine 180s and a 41.94 per cent success rate on the doubles, peaking well over 100 in sets two and three. A fourth-round meeting with Justin Hood now awaits.
Tuesday sees the fourth round continue at Ally Pally, with the likes of Luke Humphries, Michael van Gerwen, Gian van Veen and Gary Anderson all in action.
Monday evening results:
Josh Rock 4-1 Callan Rydz (round three)
James Hurrell 0-4 Ryan Searle (round four)
Luke Littler 4-2 Rob Cross (round four)