Kevin Durant couldn't keep his emotions in check. He thought his big shot caused for a big celebration. And after his 3-point bomb ripped through the net, giving his team a 15-point lead with 5:06 left on the game clock, the Oklahoma City Thunder's star looked toward his bench, put both hands in front of his waist and motioned as if he was fitting his hips with a championship belt. Big shot. Big celebration. Big mistake. It was that youthful exuberance that eventually became the Thunder's downfall. While the Thunder's 20-somethings were busy celebrating, the cagey old Dallas Mavericks were busy chipping away. Ten minutes later, the Thunder found itself on the wrong end of a colossal collapse, dropping a 112-105 overtime decision on Monday night in Game 4 of the Western Conference Finals. With the win, the Mavs secured a 3-1 series lead, a hole that only eight of 200 teams have ever climbed out of. “There's no doubt it was a tough loss,” said Thunder coach Scott Brooks when asked about the mood of his locker room after the game. “If this loss did not hurt, there's no such thing as a loss that can hurt you.” Durant refused to blame what happened here on youth. But, really, there is no other way to explain the events of Game 4. The Mavs didn't win this game. The Thunder lost it. Oklahoma City scored six points in the final 10 minutes, 6 seconds. Following Durant's 3-pointer that put OKC ahead by its largest margin of the night, the Thunder missed eight of its final nine shots in regulation while turning it over twice. The Mavs simply worked their way to the foul line, making eight of 10 in the final five mintues, to complement their 4-for-5 shooting down the stretch. Mavs forward Dirk Nowitzki sent it to overtime with a pair of free throws with 6.4 seconds left to play. No play defined the Thunder's inexperience than the final shot of regulation. After the Thunder inbounded the ball at halfcourt, Durant settled for an early 30-foot heave from the right wing. Dallas forward Shawn Marion blocked the attempt and the Mavs recovered with enough time to call a timeout with 0.7 seconds remaining. “I didn't have anything else to do,” Durant explained. “I caught the ball almost at the half-court line, seen three Mavericks in front of me and had three seconds on the (game) clock. I didn't know what else to do. I tried to get a shot up. I didn't want to run into their defense and get another turnover.” Dallas' lob pass to the basket on an inbounds play was batted away and the Thunder survived for five more minutes. But it just gave the Mavs more time to extend the Thunder's misery. The Thunder scored all of four points in the extra period, both coming off jumpers from unlikely offensive sources Thabo Sefolosha and Serge Ibaka. Durant and Russell Westbrook, the Thunder's All-Star duo, combined to shoot 0-for-5 in the overtime and had both of the team's turnovers in the frame. The offensive drought began to take on a life of its own. There were quick shots in addition to the turnovers, stall offense characterized by one-on-one play and, of all things, missed free throws. Westbrook came up empty on a trip to the stripe with 2:11 left in regulation that could have bumped the lead to nine. In overtime, the Thunder missed five of seven shots, fouled when it shouldn't have and didn't when it needed to most, allowing 8.9 seconds to run off the clock before wrapping up Mavs guard Jason Terry in the final 30 seconds. “Looking back, you could probably say that,” Brooks said when asked if his team relaxed. Reality set in following Durant's missed 3-pointer with 9.8 seconds remaining. As Jason Kidd stepped to the foul line, Durant's celebratory mood had long subsided. It was replaced with dejection. Durant kneeled just beyond the 3-point arc. His head was bowed. His eyes were open and his mind was drifting. “I let the city down,” said Durant, whose nine turnovers overshadowed his 29 points, 15 rebounds and four assists.