Argentina’s Walter Dario Matthysse made quite an impression in his United States debut Thursday night at the 4th and B Club in San Diego. He stopped Xavier Tolliver in a single round. “Matthysse was explosive and this is the type of performance we knew he would deliver after scouting him over the last year,” said Golden Boy Promotions president Oscar De La Hoya of his latest signee. “The welterweight division has a new star, and we’re ready for all comers.” The end came at 2:27 of the opening round, with a devastating right hand from the 27-year-old Matthysse sending Tolliver crashing to the canvas. Said the classy Tolliver after the fight: “He was strong; he caught me with a good shot and he is the better fighter tonight.” Santa Fe’s Matthysse (24-0 with 23 KOs), has not gone the distance since his fourth pro bout in 2003, a streak of 20 wins and one no-contest.