It took Allen Webster exactly one pitch to realize he wasn’t in the minor leagues anymore. Summoned from Triple-A Pawtucket earlier in the day, Webster soaked in the crowd at Fenway Park, got his nerves in check, and just after 7 p.m. whipped a 95 mph fastball at Kansas City Royals left fielder Alex Gordon. Webster figured he’d be taking. Gordon had other ideas, lacing a double off the Monster in left. Welcome to the majors, rookie. The good news for the Red Sox is that Webster did not let that moment defeat him. Gordon scored on an error, and then Webster proved himself worthy of the considerable hype that has come his way not so much since the Red Sox acquired him from the Los Angeles Dodgers last August, but since a dominant spring training had Sox fans dreaming of the next Clay Buchholz or Derek Lowe. “That kid has a real good future ahead of him,” catcher David Ross said. Webster did not figure in a 5-4 loss to the Royals in the second game of last night’s doubleheader. He left with a 4-3 lead after six, having allowed five hits and three runs (two earned). He walked one, struck out five and spent the bulk of the night around the plate, throwing 57-of-84 pitches for strikes. “I felt comfortable from, well, not the first pitch,” the understated Webster said with an aww-shucks chuckle. “Once I got through that first inning, things started getting smooth for me.” Webster’s only real mistakes came in the fifth, when he left fastballs up to ex-Red Sox catcher George Kottaras and Gordon. The former landed in the bullpen, while the latter barely snuck into the Monster seats for solo homers that tied the game at 3. In the process, Webster learned a valuable lesson that doesn’t sink in until the majors, where even a career .220 hitter like Kottaras can be dangerous.