Manchester United were needing some extra inspiration after battering on Reading’s door throughout a one-sided first half.
Red-hot Marcus Rashford was having no luck - but Casemiro stepped forward with a swagger and brought Old Trafford to its feet.
First, he timed a superb 55th-minute run to latch onto an Antony pass and lift the ball over Joe Lumley.
Three minutes later he lifted the roof off with a stunning 25-yard drive that was from the very top drawer.
With eight games in February including a Europa League double-header against Barcelona and two clashes against despised rivals Leeds in the League, United fans might have expected Ten Hag to ring the changes.
But they were left applauding the Dutch boss and thanking their lucky stars he didn’t rotate the brilliant Brazilian who has become a cult figure in less than six months.
Unlike some other managers, ten Hag can’t be accused of disrespecting domestic cup competitions since arriving in England.
He’s already close to one big reward with United just 90 minutes from a Wembley final in the Carabao Cup and against Reading the Dutchman went big again.
Most of his big guns were in the starting line-up against a Reading side five points off a Championship play-off place.
And Ten Hag made only one change from the team which planted one foot in the League Cup final with their 3-0 win at Nottingham Forest, with Harry Maguire getting a rare start in place of World Cup winner Lisandro Martinez.
Reading hardly had the best preparation for a trip to in-form United having lost 4-0 at Stoke.
But backed by 3,000 fans they hoped the prospect of a free hit against their illustrious opponents might bring a surprise.
United, though, quickly gained control of the game and looked threatening every time they burst forward and in the opening half-hour had 84 per cent possession.
It meant Reading lived dangerously, but somehow survived a testing opening 20 minutes.
There were scares with lively winger Antony setting up a chance for Wout Weghorst then curling a trademark shot just past the far post with Lumley scrambling.
In between Eriksen went close with a whipped free kick and Rashford fired in a stinger beaten out by Lumley from another dead ball after Tom Holmes had clattered Weghorst.
With Reading struggling to stay afloat United thought they’d scored after 35 minutes when Rashford headed over the line at the far post, but a var check ruled Weghorst was marginally offside in the build-up.
The Royals survived again when Junior Hoilett looked to have fouled Casemiro in the box but referee Darren England wasn’t impressed.
David de Gea only had four touches in the first half - but one of those was a superb save to stop Reading from almost unbelievably taking the lead through Hoilett in the last seconds before half time.
