The striker had failed to find the back of the net in the league since a win over Hibernian on February 14 but reached the milestone on Saturday.
Nacho Novo doubled the advantage before Damian Casalinuovo pulled a goal back for United as Rangers held on for the win.
With nothing at stake, both teams made mass changes for the clash at Tannadice.
Rangers were without the suspended Sasa Papac, meaning a rare start for Steven Smith, while goalkeeper Neil Alexander, Andrew Little, Boyd, John Fleck, Kirk Broadfoot and Novo were also drafted into the team after last week's title triumph.
With third spot secured, United made six changes from their defeat to Celtic and Danny Cadamarteri, David Robertson, Casalinuovo, Kevin Smith, Keith Watson and Craig Hill all started.
Rangers enjoyed the best possible start to the game when they surged into the lead after just two minutes.
The ball broke for Fleck who raced towards goal before slipping a short pass into the path of Boyd to send a low, right-foot shot past goalkeeper Dusan Pernis.
There was a further blow for United when Cadamarteri appeared to land awkwardly on his shoulder and was forced out of the action after just 11 minutes. He was replaced by Ryan Dow.
Rangers came close to adding to their lead with Novo the provider for Fleck, whose shot appeared netbound before taking a deflection off Garry Kenneth and flying wide.
Novo then squandered a decent chance of his own when he shot from just inside the box but failed to trouble Pernis.
Kevin Thomson was clearly still struggling from a head knock after a collision with Kenneth earlier in the game and he was replaced by DaMarcus Beasley with 28 minutes gone, with Fleck moving to central midfield.
Rangers were carving out the best of the chances and Novo squared for the on-rushing Boyd, but his shot lacked power and was gratefully scooped up by the United goalkeeper.
Novo's hard work paid off when he was rewarded with a goal of his own as he skipped past Sean Dillon far too easily before slotting into the far corner four minutes before half-time.
The visitors could have been further ahead when Boyd appeared to be fouled in the box by Hill in injury time but there was no penalty award from referee Stevie O'Reilly.
Rangers had the chance to add to their advantage shortly after the restart when Steven Naismith won a free-kick 25 yards out but Steven Smith curled straight into the hands of Pernis.
At the other end, the home side had a rare opportunity when David Robertson whipped an inviting ball into the box from the right only for Kevin Smith to nod harmlessly over from close range.
United were threatening again when Dow's cut-back was collected by Casalinuovo six yards out but he could not keep his shot down and ballooned it well over the crossbar.
Broadfoot could have snuffed out any chance of a United comeback when an attempt to clear a David Weir ball into the box broke to him and he volleyed narrowly past the upright.
The Tannadice side had looked more lively in the latter stages and they pulled a goal back with 10 minutes to go when Dow's corner was met by Casalinuovo, who directed a header past Alexander.
Boyd thought he had claimed his second of the day when he ran onto a Novo pass before side-footing what would have been a lovely goal past Pernis had the offside flag not been raised.
David Robertson was then booked for diving after going to ground in the box under pressure from Broadfoot as Rangers held on for the win.