WASHINGTON — Hillary Clinton may have won the first Democratic debate, but she didn’t gain any ground on chief rival Bernie Sanders, according to a CNN/ORC poll.

Clinton leads Sanders 45 to 29 percent in the national survey, which was released Monday.

Sanders’ support improved from 24 percent a month ago, while Clinton’s ticked up from 42 percent.

Vice President Joe Biden, who remains on the sidelines as he undergoes a lengthy decision-making process, saw his support drop from 22 percent a month ago to 18 percent.

The gains by Sanders came even though most Democrats who watched the debate say Clinton won.

Of those who saw the two-hour showdown, 62 percent said Clinton performed best, compared to 35 percent who selected Sanders.

Former Virginia Sen. Jim Webb, who spent much of the debate complaining about his lack of air time, scored 1 percent. The other two candidates, former Maryland Gov. Martin O’Malley and former Rhode Island Gov. and Sen. Lincoln Chafee, both came in under 1 percent.

Biden and Sanders are the only Democrats surveyed who hold a positive approval rating.

Biden’s favorability rating is 51 percent positive to 37 percent negative, while Sanders’ rating is 41-29 percent. Clinton’s favorability rating is a negative 46-50 percent as she approaches critical testimony before the House committee investigating Benghazi on Thursday.