BOSTON—When the Milwaukee Bucks scratched Giannis Antetokounmpo 90 minutes before the tipoff, Boston coach Ime Udoka worried that his team would expect an easy night against the rest of the defending NBA champions. It took the Celtics a while to snap out of it. “There’s always a natural letdown. That was the message before the game,” Udoka said after Boston beat Milwaukee 122–113 in overtime Friday night. “The other guys are going to play hard and come in with a ‘nothing to lose’ attitude, and they did.” Dennis Schröder scored a season-high 38 points—eight in overtime—as the Celtics took advantage of the reigning NBA Finals MVP’s absence to pull away. Jayson Tatum scored 27 with 11 rebounds for Boston, which has won four of five since opening the season 2–5. Tatum said that hearing Antetokounmpo was out, joining Khris Middleton, made him “locked in even more.” “Guys played more free …