Dave Matthews Band opened its summer amphitheatre tour last night at Mansfield, MAs Tweeter Center for the Performing Arts with the help of a group of close friends. As he has every night since 2005, trumpeter Rashawn Ross played with the group for most of its set and, as expected, the evenings opening act Xavier Rudd appeared on pair of aquatic-themed songs, Still Water and Dont Drink the Water. Noted saxophonist Sam Kininger, who has performed with Ross in a number of settings including Lettuce and Soulive, also jammed with the group on Jimi Thing and Louisiana Bayou. The sit-in marked Kiningers first appearance with the Dave Matthews Band since 2002. A number of years after debuting #36, #40 and #41, Matthews also offered the first full band reading of his new song #27, which he played last weekend at a ritzy private show in the Hamptons. The group will return to Mansfield, MA tonight, while Kininger will appear at Northampton, Massachusetts Bishop’s Lounge on August 17.