The two actors staged a 10-day stand-off while shooting in Mexico after one unspoken incident turned them against one another.
Sarsgaard, who is dating Gyllenhaal's actress sister MAGGIE, admits, "As the temperature rose, people would start getting a little bitchy."
Gyllenhaal adds, "If you get a group of guys together who know that they're making a war film, it can get very intense."
But Sarsgaard reveals he has a new-found respect for Gyllenhaal after the two actors cleared the air with an angry face-off.
He says, "Jake has such a huge heart... He really does want honesty above all things. We could only go for so long without being honest with each other."