Chong's big moment arrived just past the hour mark when he came on for goalscorer Mata, and the Curacao-born Dutchman enjoyed a lively and crowd pleasing debut full of flicks, energy and dangerous running. There's certainly more to come from the latest product of United's Academy conveyor belt.
The result means that Solskjaer joins Sir Matt Busby as the only Reds manager to win the opening five matches of his managerial tenure.
It wasn't the best United display of the Norwegian's caretaker era but following a hectic Christmas and New Year period, the much-changed Reds came through comfortably enough, despite some harum scarum moments that threatened a second successive clean sheet.
Perhaps understandably with a side showing nine changes that had never played together before, and featuring many fringe players, it was a ragged start to the third round tie, a repeat of the Reds vs Royals encounter from the same stage of this Cup two seasons ago.
The first chance of the contest fell to Reading on 17 minutes, when the impressive right-back Andy Yiadom burst through one-on-one with the recalled Sergio Romero, but the golden moment got the better of him and he ballooned the shot over the bar. Alexis Sanchez then went close to United's opener when he flashed his effort over the bar after a trademark run from deep.
Then came the main talking point of the half and indeed the match. Mata was scythed down in the box by the lunging Omar Richards, only for referee Stuart Attwell to play the advantage as he waved play on. Fred picked up the loose ball and fired in a finish, but - the Brazilian having been flagged offside - the ref, as replays were viewed and VAR checked and double checked, eventually awarded the spot-kick for the original foul on Mata. He dusted himself down and slotted in beyond Anssi Jaakkola for his fifth goal of the season.
It should have settled United and deflated Reading, who hadn’t won in their last previous ten games, but instead the visitors came at the Reds again. They had another glorious chance when Danny Loader was put clear. The striker rounded Romero but dallied and allowed the Argentinian to recover and put the ball out for a corner.
The Finn foiled Lukaku before bold Reading went close at the other end through Callum Harriott and Yiadom once more, as this time the advancing full-back was denied by the increasingly busy Romero.
Four minutes into added-on time, Lukaku put distance between his side and the plucky visitors.
Mata was again involved in the build-up and Alexis picked out a pinpoint pass for Lukaku to dart into the box. The Belgian’s touch took him around the keeper and he slid the ball in left-footed on the angle as he moved level with Paul Pogba and Anthony Martial on nine goals atthe top of the Reds scoring charts.
That effectively ended the tie as a contest allowing Ole to introduce Chong for Mata and Marcus Rashford for Sanchez, who picked up a knock. To their credit, Gomes' men continued to press and could have turned United's picnic into a panic when Romero tipped wide late on from half-time substitute Sone Aluko. In the end, though, the Reds saw out the closing stages in comfort and secured our place in the fourth-round hat thanks to those two first half goals.
Overall team performance: 6/10
United Faithful Man of the Match: Matteo Darmian. Solid and safe in an unfamiliar centre-back role.