"American Idol" finalist Adam Lambert performed a cover version of METALLICA's "Enter Sandman" earlier tonight (Sunday, October 17) at his concert in Auckland, New Zealand as a birthday surprise for his bass player, Tommy Joe Ratliff.Fan-filmed video footage of the performance can be viewed below. Lambert's current touring guitarist is none than Monte Pittman, who has also recorded and toured with PRONG in addition to playing guitar for MADONNA. "Enter Sandman" was featured as the opening track and lead single from METALLICA's eponymous 1991 album. The song was produced by Bob Rock, and the music was written by Kirk Hammett, Lars Ulrich, and James Hetfield. Vocalist and guitarist Hetfield wrote the lyrics, which deal with the simplest concept of a child's nightmares. The "Enter Sandman" single was certified gold in the United States for sales in excess of 500,000 copies. Acclaimed by critics, the song is featured on all of METALLICA's live albums and DVDs released after 1991 and has been played live at award ceremonies and benefit concerts. It is considered to be METALLICA's signature song to the general public. METALLICA's self-titled "black album" has sold more than 15 million copies in the U.S., according to the Recording Industry Association of America (RIAA). Colombian pop star Shakira performed a cover version of the METALLICA classic "Nothing Else Matters" during her recent North American tour.