Jeremy Affeldt has a simple explanation for an immense improvement over last season, which has made him a game-saving setup reliever a year after he was an expensive disappointment. With a shutout inning that included two strikeouts Monday night, Affeldt surpassed last year's games pitched total of 39. At season's end, manager Bruce Bochy told Affeldt he needed to be in better shape. [...] pain-free, Affeldt through Monday posted career bests in ERA (1.53), WHIP (0.934) and strikeout-to-walk ratio (3.57). Manager Bruce Bochy said Brandon Belt is making slow progress in recovery from a concussion and could swing a bat in about two days. Henry Schulman is a San Francisco Chronicle staff writer.