Not being a regular player hasn’t been part of Matt Holliday’s career until this season, when illness and injury led to diminished playing time in the final month.

“I do what I can to stay sharp timing-wise the best I can,’’ Holliday said of his work program when not in the lineup, as he wasn’t for Wednesday night’s 6-1 win over the Rays at Yankee Stadium. “Turn up the [pitching] machine velocity. Other than that there isn’t much more that I can do at this point.’’

In 15 September games (14 starts), Holliday hasn’t started more than three straight games, and Wednesday was the third time in five games the DH wasn’t in the lineup.

Asked if it was tougher mentally or physically to not be in the lineup regularly, Holliday put the Yankees ahead of his situation.

“We are trying to do something as a team,’’ Holliday said. “When I am in there, I am trying to get good at-bats and contribute.’’

Signed to a one-year deal for $13 million last winter, the 37-year-old Holliday had 47 RBIs on June 21. Seven days later, he was placed on the DL with the Epstein-Barr virus. He returned July 14 and hit a homer off Craig Kimbrel in Fenway Park. Holliday returned to the DL on Aug. 6 with a strained lower back that kept him out until the rosters expanded Sept. 1.

Since Sept. 2, Holliday has played in 15 games, gone 13-for-54 (.241) with two homers, 12 RBIs and a .719 OPS. For the season, Holliday is batting .231 with 18 homers, 63 RBIs and a .745 OPS.

With Chase Headley and possibly Aaron Judge as postseason DH options, Holliday’s roster spot could be in jeopardy.

Because the Yankees won the season series against the Red Sox, 11-8, they would be crowned AL East champs if the teams tied for first place weren’t — by rule — required to play a one-game playoff.

Nevertheless, if the blood rivals are tied for the top spot after Sunday’s action, a playoff game would be held Monday at Yankee Stadium.

The winner would be the AL East champ and the loser would play the AL wild-card game Tuesday.

“I think the value of the game is so great, they probably think it’s fair,’’ manager Joe Girardi said. “I think the record should be sufficient. If I was on the other side, maybe I wouldn’t say that. It’s just adding another game, and I think if you do play in that game, you are at somewhat of a disadvantage in the wild-card game if you lose that game. You might have to use your relievers and they might not be as effective the next day.’’

Currently, Luis Severino is scheduled to start Tuesday’s AL wild-card game, presumably against the Twins, at Yankee Stadium. But because he started Wednesday night, he could work a playoff game on Monday on regular four days’ rest.

But the Yankees’ tragic number is two with four games to play.

Girardi has gone to David Robertson and Tommy Kahnle lately in spots that used to belong to Dellin Betances. Nevertheless, the manager said if the need arose to use Betances late in Wednesday’s game, he would — and he did.

“The last couple of games, he has been pretty good,’’ Girardi said of Betances, who worked a combined three innings on Sunday and Tuesday and didn’t allow a walk, which had been the major reason for his problems. Betances worked a clean eighth Wednesday night. “His issues have been walks and he has thrown the ball much better.’’

Betances struck out Lucas Duda to give him 100 strikeouts for the season. He is the fifth pitcher in baseball history to have four straight seasons of at least 100 punchouts as a reliever. Before Betances reached that milestone, the previous pitcher to do that was teammate Aroldis Chapman, who did it from 2012 to 2015.

At 18-7 in September, the Yankees are one win away from tying the club record for most wins in the final month of the season since they went 19-9 in September 2009.