Whisenhunt’s debut spoiled as SF Giants’ losing streak hits four

SAN FRANCISCO — The arrival of the organization’s top pitching prospect wasn’t enough to stop the skid.

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.

With two vacancies in the rotation, manager Bob Melvin said pregame...