Changeups can shake magic out of musicians’ commonplace practices. Yet the Dave Matthews Band only kept unfurling surprises when that perennial headliner at Mansfield’s newly renamed Xfinity Center notched a show to remember on Saturday.

For starters, in tune with the format of this tour, DMB served as its own opening act with a 50-minute acoustic set that missed the volume but not the dynamics of its usual sound. Carter Beauford even pumped a basic drum kit behind congas and bongos as spry crowd-pleasers “What Would You Say” and “Ants Marching” buffered the mellow “I’ll Back You Up” and a jaunty blues cover of Sixto Rodriguez’s “Sugar Man.” Though the focus of the sold-out crowd wavered as fans settled in with the sun still up, people throughout the venue basked in a soundtrack and vibe that matched the picture-perfect weather.

With casual fans likely satiated by the night’s initial song mix, singer Matthews and his band dug into diehards’ dreams, launching a second set with back-to-back nuggets “Granny” and the elusive, hypnotic “Seek Up.” One of DMB’s jazziest opuses when the group broke beyond the jam-band scene two decades ago, that piece dropped out of rotation after the 2008 death of saxman LeRoi Moore, but emerged in full bloom as a near-20-minute ride. Matthews’ skeletal guitar figure laid the base for Rashawn Ross and Jeff Coffin to patiently trade off solos on trumpet and soprano sax until they erupted in tandem waves against Beauford’s multi-cymbal slams before the first vocal crept in. Then violinist Boyd Tinsley added a ghostly, sawing solo to extend the early-set adventure, which was complemented with spacy, laser-swept lighting more akin to Phish or Pink Floyd.

After the set jumped to sensory assault with stage-wide backing video and the music toggled between the bombastic (“So Right,” “Don’t Drink the Water”) and the benign (“Satellite”), Matthews sprang the night’s most unexpected treat – and climactic highlight. The Lovely Ladies – DMB’s former backup singers Tawatha Agee and Cindy Mizelle, with newcomer Sharon Bryant – came out to join the band for the first time since 2001 (Tinsley later tweeted that the singers would pop up for a few other dates). The trio got a rock-star reception from the crowd, which spontaneously began to sing “Hani, Hani, come and dance with me” from old song “#36” over the band’s developing groove. And the Ladies graced both the country ballad “Long Black Veil” and the syncopated R&B shaker “Stay (Wasting Time),” sealing a wicked kickoff to summer at the shed.