The 18-year-old striker skilfully won a second-half penalty which he slid past fellow teenager Jamie Newman in the East Stirling goal.
The fourth-round tie had offered potential problems for United in the shape of a fierce wind and the artificial surface at Ochilview, but goals from Prince Buaben, Darren Dods and Jon Daly killed it off before half-time.
Former United hero Jim McInally has turned Shire from the worst league team in Scotland to Third Division promotion contenders.
However, apart from a brief spell of pressure in the first period, they were outclassed by an in-form United.
Levein was without the suspended Lee Wilkie and injured Scott Robertson but United quickly took control after an early scare.
Craig Donaldson played Colin Cramb clean through as United's offside trap failed, but the striker chipped over from 18 yards with only Lukasz Zaluska to beat.
Russell, who scored twice against Shire earlier in the season during a loan spell with Forfar, soon set up a good chance for Daly but the Irishman was off target from 12 yards.
Russell then failed to get a strong enough touch to steer the ball past the advancing Newman, a 17-year-old who was making his debut after Falkirk recalled loan keeper Jamie Barclay.
Buaben shot just over from 20 yards after a positive run by Russell, and the midfielder then put United ahead in the 15th minute.
United built play well down the left and Buaben fired into the bottom corner from 20 yards after a lay-off from Daly.
The visitors looked well in control immediately after the goal but Shire went on to enjoy a decent spell of pressure.
Andy Rodgers shot two yards wide from the edge of the box after a dangerous Donaldson corner and David Dunn used the wind at his back to shoot from a 40-yard free-kick, with the ball deflecting two yards wide.
Dunn's subsequent far-post corner was headed into the side-netting by Brian Graham and Michael Bolochoweckyj soon fired just wide of Zaluska's near post after the United defence hesitated following a long throw.
However, the visitors stepped up a gear and Daly headed just over the bar from Russell's brilliant cross.
They doubled their advantage in the 40th minute when Dods nodded home from close range after Paul Dixon had curled a corner into the six-yard box.
And Daly headed home powerfully from 10 yards two minutes later following an inviting cross by Sean Dillon.
Newman blocked Willo Flood's low drive from inside the box as the visitors threatened to run away with the contest before the interval.
Shire struggled to get out of their own half as the second half began and Russell grabbed his first United goal in the 55th minute.
The teenager was brought down by Craig Tully fter jinking his way into the box, and his penalty just evaded the outstretched hands of Newman to find the corner of the net.
United lost Dods to a head knock before substitutes Danny Swanson and David Robertson added some urgency to their midfield late in a low-key second half.
But United's long-range shots were mostly carried over by the wind, although Robertson's 20-yard strike brushed the outside of the post.
And Newman pulled off a good injury-time block from Daly after Russell had slipped the ball across the face of goal.