WASHINGTON, Nov 12 (AFP) - President Joe Biden's Democrats retained control of the US Senate on Saturday, a remarkable midterms election result that defied predictions of a Republican win over both houses of Congress.

Midterms traditionally deliver a rejection of the party in power, and with inflation surging and Biden's popularity in the doldrums, Republicans had been expecting to ride a mighty "red wave" and capture the Senate and the House of Representatives.

But the wave never got much beyond a ripple and on Saturday US networks called the key Senate race in Nevada for Democrat incumbent Catherine Cortez Masto, giving the party the 50 seats it needs for an effective majority.

The win clinches Democratic control in the Senate as Vice President Kamala Harris can cast the tie-breaking vote if the upper chamber is evenly split 50-50.

"I feel good and I'm looking forward to the next couple years," Biden said of the result, speaking at a meeting of Southeast Asian leaders in Phnom Penh on Sunday.

One Senate race remains up in the air -- a runoff in Georgia set for December 6, in which the Democrats could add to their majority.

The result in the House of Representatives still hangs in the balance, and while Republicans are slightly favored to take control, it would be with a far smaller majority than they had envisaged going into Tuesday's election.

Senate Majority Leader Chuck Schumer was quick to ring in his party's win, tweeting the result was a "vindication" of Democrats' achievements.