Merkel, 63, shot back: “We had a very dramatic situation then ... There are times in the life of a chancellor when she has to decide.”
The Social Democrats are lagging Merkel’s conservatives by some 13 percentage points ahead of the vote, in which she is seeking a fourth term.
Schulz, 61, has called Merkel “aloof” and attacked her on a range of issues but failed to dent her lead. The debate is seen as one of his last chances to shift the momentum.
Merkel’s 2015 decision to open Germany’s borders to hundreds of thousands of refugees, many fleeing war in the Middle East, cost her support but she has since bounced back.
The first half of the debate was dominated by a discussion about migration and integration.
Schulz, a former European Parliament president with no national government experience in Germany, said he would stop membership talks between Turkey and the European Union if elected chancellor.
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