Edwin Ríos lifted the Los Angeles Dodgers to a 4-2, 13-inning win over the Houston Astros on Wednesday with a leadoff two-run homer, a feat that was impossible before this strange, shortened Major League Baseball season.

The inning began, like the three that preceded it, with a runner on second base, one of the significant modifications to the MLB rule book agreed to by the league and the players’ union in the interest of health and safety as they attempt to play amid the novel coronavirus pandemic.

The extra-inning rule was also utilized Wednesday in Washington, where the Nationals, who were playing as the road team in their own ballpark, defeated the Toronto Blue Jays, 4-0, in 10 innings. (Confusing, we know.) One week into the season, here’s a closer look at the extra-innings rule and how it’s worked so far.

What is the rule?

During the regular season only, if nine innings are completed and the game remains tied, every subsequent half-inning will begin with a runner on second base. The runner on second will be the player in the batting order — or a substitute for such player — immediately preceding that half-inning’s leadoff hitter.

On Wednesday, for instance, Kiké Hernández made the final out for the Dodgers in the top of the 12th inning and began the 13th inning on second base when Ríos came to the plate. In D.C., Emilio Bonifacio started the top of the 10th inning on second base after entering the game as a pinch runner for Starlin Castro, who made the Nationals’ final out in the ninth inning. Castro would not have been allowed to reenter the game if it continued.

Isn’t that unfair to the pitcher and those who have him on their fantasy teams?

It puts the pitcher in a difficult position, but the runner on second doesn’t count against his line. For scorekeeping purposes, the designated runner is considered to have reached on an error, though no error will be charged to either team. If the designated runner scores, it’s considered an unearned run.

Why was the rule added?

With teams scheduled to play 60 regular season games in 67 days, and with heightened concerns about keeping players healthy during the pandemic, the league would like to limit the number of games that last multiple extra innings. MLB has been experimenting with the extra-inning rule throughout the minor leagues since 2018. According to data from Baseball America, 73 percent of extra-inning minor league games produced a winner after one extra inning since the rule was enacted. In the two years before the new rule was introduced, only 45 percent of extra-inning games ended after one extra inning.

Why not just end the game in a tie?

Good question. That’s what they do after 12 innings in Japan and South Korea, where the KBO-leading NC Dinos are 44-22-2.

Isn’t it rare for a game to go beyond 10 innings anyway?

According to FanGraphs, 113 games, or 4.6 percent of the 2,429 major league games played last season, reached the 11th inning. Ninety-eight percent of all MLB games in 2019 ended in the 11th inning or earlier.

Has the rule been effective this season?

Through the first week, seven games have gone extra innings. Of those games, five were decided in the 10th inning, one was decided in the 11th and one was decided in the 13th. It’s a small sample size, but the first week of the 2019 season also featured seven extra-inning games, with three decided in the 10th inning, three decided in the 11th and one decided in the 13th.

So, what’s the best strategy for a team in extra innings?

You might think that the new rule would encourage teams to sacrifice bunt, but as The Post’s Neil Greenberg points out, it’s not a winning strategy for the visiting team. A home team that sacrifices a runner from second to third with no outs in a tie game increases its chances of winning only slightly, from 81 percent to 83 percent.

“I didn’t want to bunt,” Nationals Manager Dave Martinez said of his strategy on Wednesday. “We’re playing on the road. I wanted these guys to swing the bat. But they worked two great at-bats to get on base. That’s a testament to just teamwork, and getting on for the next guy.”

In seven extra-inning games this season, there have been as many walk-off grand slams (1) as successful sacrifice bunts.

What do players think of the new rule?

While some baseball purists decry the new rule as gimmicky, the reaction among the players is mixed. Cleveland Indians pitcher Mike Clevinger, for one, is not a fan, and tweeted that the rule is the “whackest s---" he’s ever seen.

“This isn’t travel ball,” Clevinger said after the Indians lost to the Kansas City Royals, 3-2, in 10 innings on Saturday. “This isn’t Perfect Game. You know how hard it is to get a runner on second base off the back end of any bullpen, how incredibly hard that is? And now all of a sudden you just get a guy on second base with a guy like [Indians reliever James] Karinchak on the mound. I’m not happy about it. I’m sure when other teams face the situation and this happens to them, you’re gonna get similar reactions.”

''It’s cool,'' Clevinger’s teammate, Francisco Lindor, said after the same game. ''It’s kind of Little League-ish, but I like it.''

''I love it,” Royals Manager Mike Matheny said. “I hope we do it tomorrow. Though actually that’s not true. I hope we have a bigger lead. I know I have been a proponent for it, and I know baseball traditionalists are rolling over right now.''

How about some advice for those keeping score at home?

Nationals play-by-play man Bob Carpenter tweeted a photo of his scorecard from Wednesday’s game. He used a yellow highlighter to denote the designated runners in each half-inning.

Will the rule remain in place after 2020?

The plan is for the extra-inning rule to go away in 2021, but there’s a chance it could become permanent, along with the universal designated hitter, when the CBA expires after next season.

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