Robert Gesink of the Netherlands won the grueling sixth stage of the Tour of Switzerland and claimed the race leader's jersey on Thursday while Lance Armstrong showed he is returning to top form by finishing fifth.

Gesink, who trailed race leader Tony Martin by 27 seconds before Thursday's stage, attacked 14 kilometers from the finish on the third and last climb of the day to claim a solo victory ahead of a group of eight riders that was led by Rigoberto Uran and included Armstrong.

The American seven-time Tour de France winner faced his stiffest test since last year's Tour during the 213.3-kilometer ride between Meiringen and La Punt that included three major Alpine climbs.

"It was a hard day. To be honest, I suffered in the beginning of (the last climb) the Albula," 38-year-old Armstrong told reporters at his team bus. "I couldn't find my rhythm. I kept trying, to find my own tempo and some acceleration so I didn't lose the pace. Overall I'm pretty happy."

Armstrong, whose season has been hampered by illness and a crash, crossed the line 42 seconds back. He moved up to 7th overall, 55 seconds behind Gesink, who now leads Uran by 29 seconds.

No one was able to follow Gesink when he attacked in the Albula, where Martin and Swiss star Fabian Cancellara were dropped. The 24-year-old Rabobank rider reached the summit alone and raced strongly in the downhill to La Punt.

Friday's seventh stage is a 204.1-kilometer ride from Savognin to Wetzikon featuring three climbs. The race ends Sunday with a time trial.