Papiss Cisse's close range header with 19 minutes remaining breathed life into an edgy encounter at St James' Park, but despite constant pressure they were unable to find the second goal that would have sent them through.
That search left them exposed at the back, allowing Eduardo Salvio to level in injury time.
"They are a good side, you can't let them get the lead against you," he told Britain's ITV.
"We defended well in the first half, kept it tight, looked to try and nick a goal and almost got one just before half-time.
"The second half we were going to... see if they could cope and they couldn't really, we had two or three big chances at one-nil.
"But I can't ask for anything more... from the players, I thought they were excellent tonight."
Chances were few and far between in the first half, with the best falling to Benfica's Nicolas Gaitan, whose goalbound shot was blocked by Massadio Haidara after keeper Tim Krul had lost possession on the edge of his goalbox.
