As Mariano Rivera prepares to retire, the closer's farewell tour has become a central subplot to the season. Major League Baseball's all-time saves leader has been greeted warmly in each of his road stops, and the Yankees held a ceremony of their own to honor Rivera's illustrious career on Sunday.

Rivera will be the last active player to regularly wear uniform No. 42, with the number having been retired throughout MLB in 1997 to honor the achievements of barrier-breaking great Jackie Robinson. During his 19-year big league career, Rivera has also chiseled his own mark on the number's legacy. In honor of Rivera and his contributions, MLB.com is commemorating 42 notable moments from Rivera's career -- the 42 Days of Mo.

When Mariano Rivera closed the door against the Angels on Sept. 11, 2011, for his 40th save of the season, there was not much extra fanfare. After all, Rivera had already reached the 40-save plateau in seven previous seasons and this particular save put him on the brink of a much greater milestone.

Two days later, Rivera recorded his 41st save and, more importantly, No. 600 for his career. He became just the second player to reach the 600-save mark, joining legendary closer Trevor Hoffman, yet Rivera's 599th save carried plenty of significance itself.

It was that save prior to No. 600 that catapulted Rivera past Hoffman as the oldest closer to reach the 40-save benchmark in a single season -- a record that Rivera, himself, has since broken. That first time around, Rivera became the first closer to record 40-plus saves at 40 years of age or older.

Rivera notched his 40th save in 2011 at the age of 41, eclipsing Hoffman's previous record, which he had set at the age of 39 -- just 23 days shy of his 40th birthday.

Though longtime Yankees catcher Jorge Posada was not behind the dish for Rivera's 40th save that season, witnessing the feat was nothing new. Posada had caught Rivera's 40th save in three previous seasons and been his teammate for each of the other four years. Yet when Rivera became the oldest pitcher to reach that mark in '11, Posada knew he was seeing something that may never happen again.

"The best ever. I keep saying the same thing over and over again, and it sounds repetitious every time I talk about Mo, but it's true," Posada said at the time. "There's nobody [who's] ever going to get close to what he's been able to achieve, because there's nobody better. It's just that simple."

To date, the only player to push Rivera's record as the oldest player to record 40-plus saves in a single season is, not surprisingly, himself. Entering play Tuesday, Rivera had tallied 44 saves this season, the same amount he finished with during his record-setting 2011 campaign. It was earlier this month that Rivera raised the bar on his own record, capturing save No. 40 at the age of 43.

With a perfect inning against the White Sox on Sept. 3, the legendary closer reached the 40-save mark for a ninth time, matching the record previously held solely by Hoffman. Despite the company in that category, Rivera's longevity has been unprecedented as demonstrated by the record he set on Sept. 11, 2011 -- and broke himself two years later.

Though the focus at the time was centered mostly around Rivera joining the 600-save club in his next outing, the significance of that 599th was likely overlooked. After all, Rivera becoming the oldest pitcher to reach 40 saves in a single season seems as if it, too, will be a very difficult record to break -- for anyone not named Mariano Rivera, that is.