Crucible (kroo-suh-buhl): A severe, searching test or trial.

As recently as three weeks ago, it didn’t seem like the Yankees would have a “severe, searching test or trial” moment during the regular season. Their lead over the second-place Baltimore Orioles was a full 10 games on July 18, a comfortable margin even without a healthy Andy Pettitte or Brett Gardner. Since then, the Bombers have gone 10-13, lost A-Rod until late September, had Sabathia go back to the DL a second time, seen their lead dwindle to 4.5 games, recovered to their current 5.5-game lead, and come to grips with a five-man rotation that currently includes Freddy Garcia and David Phelps.

This week brings the AL-leading Texas Rangers for a four-game set, followed by three games against the Red Sox, who are aggressively mediocre this year but always dangerous against the Yankees. The Yanks are catching a break in avoiding Texas ace Yu Darvish and may actually benefit from facing a de-clawed John Lester (6-10, 5.20 ERA) and Josh Beckett (5-9, 4.97 ERA). On the other hand, David Phelps may be starting twice this week, and one of the many things we’ve learned about the Yankees this year is that Phelps is not a major league starter, not yet.

The Yankees moved to shore up their increasingly short-staffed rotation by signing veteran Derek Lowe to a major league contract. The team’s brass said Lowe will pitch out of the bullpen, but I’m not buying it. Since 2002, Lowe has appeared in 357 games and started 355 of them. A Saturday start in Phelps’ place is not out of the question.

Tampa Bay has seven road games against the Mariners and Angels this week, the team’s last West Coast road trip of the season and a potential bump in the road. Baltimore, meanwhile, hosts Boston for three games and then will play a three-game weekend set in Detroit, which is fighting for a playoff berth of its own. The Yankees could be two games up at the end of this week; they could also be nine up. Either way, it’s gut-check time in the Bronx.

The big week kicks off tonight, with Phelps opposing Texas’s Ryan Dempster (recently acquired from the Cubs, of the 33-inning scoreless streak fame). Check back here every day for a Crucible Week recap and a live-tweeting session from the Stadium on Wednesday night.