The Portuguese gave away a penalty but, after Gareth Bale's equaliser, the Ballon d'Or holder then went on the rampage at the Santiago Bernabeu
Having scored a hat-trick in the 8-2 mauling of Deportivo La Coruna on Saturday, the Portuguese was again in imperious form as he went one better on Tuesday.
He converted two penalties on his way to a four-goal haul as Real once again produced a dazzling display.
Ronaldo's night had hardly begun as he would have wished - he was at fault for the 15th-minute penalty that gave Elche a shock lead through Edu Albacar.
But a wounded Madrid - and Ronaldo in particular - rallied, with three quick goals of their own through Gareth Bale and a double from the FIFA Ballon d'Or winner to lead at the break.
His third came with 10 minutes remaining before the fourth - a typically cool finish from Bale's pass - arrived in injury time, as Elche simply had no response.
After conceding eight goals in four La Liga matches, Iker Casillas was dropped in favour of Keylor Navas in goal for Real but 15 minutes into his debut the Costa Rican was picking the ball out of his net after Ronaldo had conceded a penalty.
The Portugal international was punished for making contact with Pedro Mosquera when clearing a corner and Albacar lashed the spot-kick into the top corner, giving Navas no chance despite the goalkeeper diving the right way.
Elche's lead only lasted five minutes, though, as Madrid came surging back into the game with three goals in 12 minutes.
James Rodriguez created the first after 20 minutes with a pin-point cross from the left that Bale met with a glancing header, although Manu Herrera should have done better in the Elche goal as the ball slipped under his grasp.
Real went ahead for the first time eight minutes later when they were awarded a penalty of their own - Mosquera adjudged to have brought down Marcelo.
Ronaldo 's emphatic spot-kick gave Herrera no chance and four minutes later the forward scored again with a perfectly placed header.
Marcelo made progress down the left before firing a cross in towards Ronaldo , who outjumped Sergio Pelegrin and headed the ball into the bottom corner.
Chances continued to come for the hosts but Sergio Ramos, Toni Kroos and Ronaldo were all denied by Herrera before half-time.
Both sides had early sights of goal after the break but Coro and Ronaldo were both wayward with their finishing as they blazed over the crossbar from inside the penalty area.
Herrera was called into action after 66 minutes when a quick free-kick from Kroos gave Ronaldo a clear shot at goal and despite the wall collapsing in front of him, the goalkeeper made a good save with his feet.
With 10 minutes remaining, Madrid were awarded a second penalty of the match as substitute Mario Pasalic felled Ronaldo .
Having dusted himself down, the 29-year-old took the spot-kick himself and once again gave Herrera no chance as he completed his hat-trick.
However, Ronaldo was not finished there and, having received a through-ball from Bale in stoppage time, he poked the ball past Herrera to secure Madrid an emphatic win.