Top seed Ben Shelton is out of the ASB Classic.  The American has fallen at the quarter-final stage, beaten in straight sets by Sebastian Baez (Argentina) on Friday. World No 39 Baez, who is the seventh seed here, is on a hot run after winning all three United Cup matches to start the week. But it was a strangely off-colour display by world No 8 Shelton, who struggled to build any momentum in the 7-5, 6-3 loss.  It’s Shelton’s first defeat (from 13 matches) against Argentine players and just the third time in 21 attempts that Baez has beaten someone ranked inside the top 10.  Rain halted the match on Thursday night, with Baez ahead 7-5, 0-1. The contest continued in bright sunshine on Friday, with the players walking on to court at 12.15pm. But the signs were not good from the start, as Shelton was broken in his first service game after a loose backhand.  Baez seemed to have an answer for everything, at one stage running down a drop shot from the opposite corner of the court. Shelton was trying to bring his full armoury, with some wicked serves and big shots, but was erratic and plagued by constant errors.  He had a chance to break back at 3-4 down, but Baez defended the opportunity before the pivotal ninth game. Shelton was a bit careless, while Baez managed another of his trademark drop shots and the American was soon in trouble at 15-40.  The 23-year-old saved one match point with a booming 197km/h serve but that was the last of the resistance. On the next point he shanked a backhand, with the ball flying off the frame and into the air, which summed up his unfortunate day.  Michael Burgess has been a Sports Journalist for the New Zealand Herald since 2005, covering the Olympics, Fifa World Cups, and America’s Cup campaigns. He is a co-host of the Big League podcast.