Rep. Bill Cassidy (R-La.) defeated Sen. Mary Landrieu (D) in Louisiana runoff election for U.S. Senate seat. (Reuters)

Republicans put the finishing touches on a triumphant midterm election by picking up a ninth Senate seat Saturday when Rep. Bill Cassidy (R-La.) defeated Sen. Mary Landrieu (D) in a runoff election.

Landrieu’s loss means there will be no Democratic senators from the Deep South when the new Congress is sworn in early next year. It will end Landrieu’s tenure in the Senate after three terms and deprives Democrats of holding a single statewide elected office in Louisiana.

With most precincts reporting, Cassidy led Landrieu by about 14 percentage points. The Associated Press called the race for Cassidy shortly after polls closed in the evening.

Cassidy’s win comes after Republicans swept into power in the Senate on Nov. 4, picking up eight Democratic-held seats without surrendering any of their own. In Louisiana’s all-party Senate primary that day, no candidate received a majority of the vote, triggering the runoff.

Louisiana voters also decided two open U.S. House races Saturday. Republicans held both seats. The GOP will start the next Congress at least matching its largest majority since World War II.

In the race for Cassidy’s 6th District seat, Garret Graves (R), a former coastal adviser to Gov. Bobby Jindal (R), defeated former governor Edwin Edwards (D), a felon and well-known figure in the state.

In the deeply conservative 5th District, Republican physician Ralph Abraham defeated Monroe Mayor Jamie Mayo (D).

In his victory speech, Cassidy said voters “chose a government that serves us but does not tell us what to do.”

In her concession speech, Landrieu told supporters, “Tonight we have so much to be proud of — a record of courage, honesty and integrity.” After her speech, Taylor Swift’s “Shake It Off” played on the loudspeakers.

Landrieu spent Saturday much as she spent the rest of her runoff campaign: trying to boost Democratic turnout. After casting her ballot in New Orleans with her family in the morning, she turned her attention to canvassing.

Cassidy, who kept up a much more limited public schedule in the final days of the race, cast his ballot in Baton Rouge last month during early voting.

Landrieu spent the final week barnstorming the state, holding three or four events per day and traveling from one end of Louisiana to the other. She ran ads aimed at boosting turnout among African American voters, who supported her overwhelmingly in the primary.

Conservative groups dramatically outspent Democratic organizations on TV and radio ads during the runoff campaign. With no hope of restoring their Senate majority and still reeling from the disappointing losses of Nov. 4, national Democratic groups effectively abandoned Landrieu in the runoff.

Days before the election, Landrieu said she was “extremely disappointed” that the Democratic Senatorial Campaign Committee decided to cancel its ad reservations.

The conservative groups and Cassidy repeatedly sought to tie Landrieu to President Obama and his record. Obama is very unpopular in Louisiana, polling shows.

The spending disparity allowed Cassidy to coast though the final week of the race and keep a low profile. After appearing at the final debate Monday, Cassidy did not resurface on the campaign trail until Friday, when he rallied support with Iowa Sen.-elect Joni Ernst (R).

Landrieu accused Cassidy of hiding from voters and questioned his record as a part-time physician and teacher at Louisiana State University.

After a local blog published his time sheets, raising questions about whether he fulfilled his requirements, the university said it would look into the matter. Landrieu repeatedly said Cassidy may have committed payroll fraud. He insisted he did nothing wrong.

Coming so late in the race, the revelations never seemed to break voters’ confidence in Cassidy in a meaningful way.