Joe Nathan’s first season with the Tigers will be his 20th season in pro baseball. The most soaring moment and most troubling moment in that long journey came less than six months apart. On Oct. 6, 2009, in the AL Central tiebreaker game, Nathan escaped trouble to hold off the Tigers in the eighth and ninth innings and keep the game tied. Minnesota won in the 12th inning. Nathan considers it the most exciting game in which he has ever played. In spring training the next year, Nathan felt discomfort in his pitching elbow. A few weeks later, he decided to have the “Tommy John” surgery, in which a ligament would be transplanted from his left wrist into the elbow. He would miss all of 2010 season, and he couldn’t be sure if he would remain what he’d been for the previous six years: one of the best closers in baseball. On Wednesday, the Tigers signed Nathan, who recently turned 39, to a two-year contract worth $10 million per season. Moments after his introductory news conference, Nathan was asked, “On the day you found out you needed the Tommy John surgery, if you had been told you would be getting this good of a deal with this good of a team that carries you through age 40, what would you have said?” “I would have said you were crazy,” Nathan replied. He was also trying to take in that the Tigers, whom he wanted to play for, reciprocated his strong interest. Nathan came back so well from Tommy John surgery that it’s hard to remember he had it. In the last two seasons with Texas, he has averaged 40 saves. Many pitchers like Nathan have come back strong from Tommy John surgery, and some throw harder than before the operation. That’s not true for Nathan. He acknowledges he doesn’t throw with the same zoom he did when he got into the closing business with Minnesota in 2004. But he still throws hard, and he mixes in a variety of pitches, accented by that knowledge from nearly two decades in the pro game. Nathan could be the pitching equivalent for the Tigers of Darrell Evans: the veteran who comes to the Tigers late in his career and then maintains his peak up to 40. At age 38, in 1985, Evans won the AL home-run title. At age 40, he hit 34 homers and drove in 99 runs.