As usual, Serena Williams stands alone.

The 23-time Grand Slam winner is again the last American left at the U.S. Open following Taylor Townsend’s 6-1, 4-6, 6-2 fourth-round loss to 15th-seeded Bianca Andreescu early Tuesday morning at Arthur Ashe Stadium.

Andreescu will face 25th-seeded Elise Mertens in her first-ever grand slam quarterfinals — the first by a Canadian at the U.S. Open since 1992 — while Townsend leaves with the best two weeks of her young career.

After reaching the third round of the 2014 French Open in her Grand Slam debut, Townsend had failed to reach the third round of a major in 15 straight main draw appearances. Then, the 23-year-old won three matches in U.S. Open qualifying and another three over the past week to reach the second week at a major for the first time.

“She had an incredible run. Coming from [qualifying], getting to the fourth round is truly incredible,” Andreescu said. “She has a different game than anyone and I’m sure she’s gonna get far.”

Coming off a massive upset of Simona Halep, Townsend initially was punished by Andreescu for her old-school serve-and-volley attack which stymied the fourth-seeded Wimbledon champion.

Then Townsend — the world’s former top-ranked junior and currently the world’s 116th ranked player — adjusted, winning the second set’s first three games and controlling the pace from the baseline. After evening the match by breaking the second set’s final game, Townsend walked to her chair and motioned to the crowd, screaming “Come on!” while being showered with cheers.

“It wasn’t easy, but I heard some Canadian fans here and there, which is nice in tougher moments,” Andreescu said. “I tried not to pay attention to that, but it’s hard when it’s everyone. I’m glad with how I managed to keep my cool.”

Townsend was broken to open the third set and Andreescu’s superior ball striking continued tilting the match in her favor, as Townsend won just 48 percent of points on her first serve.

While trailing 5-1 in the final set, Townsend saved four match points, and kept the sparse, late-night crowd hopeful her run would provide its greatest moment yet. Andreescu quickly ended any fantasy of a comeback, winning four straight points on serve to take the match.

Townsend left with nearly as much money from her time at the U.S. Open ($280,000), as she had made since the beginning of the year ($331,000). Andreescu left with the best feeling of her career.

“This year has been the best year of my life so far,” Andreescu said. “I’ve never felt this confident before.”