Jason Day bumps Jordan Spieth from No. 1 in golf’s version of musical chairs

Jason Day and Jordan Spieth were not in the lineup for the PGA Tour’s 2015-16 wraparound season-opener in wine country last week but, thanks to the quirks of the system, the two players once again exchanged places atop golf’s official world rankings.

Day, who held the slot for one week before Spieth replaced him as No. 1 in September, took the spot back on Monday, as formerly top-ranked Tiger Woods continued his slide into oblivion and 334th place.

Rory McIlroy, who finished a lackluster T26 at the Frys.com Open on Sunday, maintained his hold on the third seed, with big-hitting Bubba Watson, appropriately, batting cleanup.

A similar see-saw battle for mathematical supremacy is taking place among the women, as Lydia Ko has another chance this week in Taiwan to surpass Inbee Park in the Rolex Rankings. Ko appeared poised to do so at last week’s tourney in South Korea, where she took a share of the 54-hole lead into the final round but stumbled down the stretch to a T4 finish.

Lexi Thompson moved up from fifth to fourth with her come-from-behind, one-shot victory at the LPGA KEB Hana Bank Championship. But it was Amy Yang, who shared fourth with Ko and Gerina Piller, who lit up the highlight reel by running off nine straight birdies on her way to a back-nine 27.

Yang rose from ninth in the world to No. 8 on the back of all those birdies.

Back on the PGA Tour, rookie Emiliano Grillo advanced from 72 to 36 after nailing the Frys win in his first tour start. Runner-up Kevin Na jumped to 24 from 33.

You don’t need a graduate degree in algebra from MIT to understand the men’s rankings, which are based on a two-year rolling weighted algorithm, but it wouldn’t hurt. Just know that Day won his first major at the PGA Championship in August and five more tour events this season, skipped past Spieth on the rankings roster on September 21 and fell back after the reigning Masters and US Open winner prevailed at the Tour Championship.

For true numbers geeks, Day has the slimmest of advantages, with a 12.42 points average to Spieth’s 12.39. McIlroy was No. 1 to start the year but an ankle injury that forced him to miss title defenses at the British Open and WGC-Bridgestone Invitational doomed his chances to remain at the pinnacle.

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