Carson Whisenhunt overcame a rocky start as he allowed four runs over five innings in his major-league debut, but the Giants’ losing streak hit four games as they fell to the Pittsburgh Pirates 6-5 on Monday night at Oracle Park. With Thursday’s trade deadline looming, San Francisco has lost 10 of its last 12 games.

SAN FRANCISCO — The Giants have selected the contract of left-hander Carson Whisenhunt, the top pitching prospect in their organization, ahead of his first career start on Monday night at Oracle Park against the Pittsburgh Pirates.

Whisenhunt (ND, 0-0, 7.20 ERA) surrendered four runs in five innings, struck out out three, and walked two before handing a tie game to the bullpen. Carson Seymour (L, 0-1, 4.00 ERA) entered in the seventh and gave up two runs, extending the Giants losing streak to four straight, and 10 of their last 12.