Fener were comfortable 3-1 winners on Sunday to leave Newton fighting for his job at Trabzonspor.
The former Chelsea coach has overseen a poor start to the season and went into the Fener game already under pressure. A board meeting to discuss Newton's position is scheduled for later in the week.
Newton said, "I am really disappointed. We were very good in the first half. However, we had a nightmare in the second period.
“We play good football but sometimes we cannot get the results we want due to simple mistakes that should not happen.
"You should not lose concentration as much as three goals in a row."