OAKLAND -- Entering the Oakland stretch of the Battle of the Bay series, the A's had everything working for them. They had the momentum after sweeping the top team in baseball, the Dodgers. They had the home field advantage -- the Giants hadn't won a game here since June 24, 2009. They even said they were excited to take on their cross-bay rivals. They got off to a great start, scoring three runs on two-time Cy Young-award winner Tim Lincecum. They even had a two-run lead going into the ninth inning -- they had it all working. Then it all came crashing down. I guess that's the way the cookie crumbles. The A's new closer Ryan Cook gave up four runs without recording an out in the ninth inning, as the Giants went on to win 5-4. Cook has been a phenomenal find for the A's. The right-handed pitcher, 23, had been rock-solid since taking over the closer's role, going four for four in save opportunities. Entering Friday, he had only allowed a run in 29 of his 30 appearances. "Cook is not going to go the whole year and not blow a save," A's manager Bob Melvin said. "Too bad it had to happen tonight." Cook worked himself into trouble immediately. He walked Buster Posey on four-straight pitches, then put the tying run on first by walking Pablo Sandoval. Next, Brandon Belt -- who had been hit in the hand by a pitch in the seventh inning -- came to the plate. He laced a ball to left field that landed just outside the outstretched glove of Collin Cowgill, who laid out for the ball. Posey and Sandoval came around to score, tying the game at three."It's been my hex all year, putting guys on," Cook said. "It came back to bite me tonight."I knew he was a little bit erratic," Belt said of Cook. "If he threw anything in the strike zone I was going to pounce on it.The A's may have lost more than the lead on Belt's double. Cowgill injured his left ankle on the diving attempt. He could have possibly played it safe and let the ball fall, keeping it in front of him. That would have only allowed one run to score, preserving the lead. But as Melvin explained it would have still left the A's in a bad situation. "I don't have any problem with him trying to catch that ball." Melvin said of the diving attempt by Cowgill. "If he catches that ball it's an entirely different game."After Cook departed the game, Sean Doolittle entered and gave up RBI singles to Hector Sanchez and Gregor Blanco, giving the Giants a 5-3 lead. Both runs were charged to Cook. The ninth inning meltdown for the A's lead to the Giants snapping a six-game losing streak in Oakland. They had plenty of opportunities to put the game away too. In the first inning, they had Lincecum on the ropes. With three runs already scored, and the bases loaded with no outs, Lincecum struck out Brandon Moss, Kurt Suzuki, and Cliff Pennington to escape the inning. After the third run scored, Lincecum became a completely different pitcher. He retired 17 of the next 19 batters he faced, striking out eight.I was trying to channel that madness and stop worrying about the expletive happening behind me, Lincecum said. If there were any positives to point to for the A's, it's the performance of Jarrod Parker. The 23-year-old righty, was inline to win the game allowing just one run in six innings."I got outs and made pitches I need to," Parker said. "Overall it was a good outing. Sucks we didn't win. Obviously losing is not what we want, and it's a tough game but we'll bounce back."