On Sunday, Luzhniki Stadium will be the site of what is likely to be the defining match of the season. Rubin Kazan, atop the Premier League stable by one point, is hosted by Spartak Moscow, sitting second in the league.

The previous meeting in Kazan (April 25, the sixth round of the season) saw Spartak hand Rubin their first loss of the season, a 2-0 victory that saw Spartak double the number of goals Rubin had allowed in the preceding five matches. Alex assisted on both goals, the second scored by Welliton. The match featured nine cards, six issued to Spartak, yet managed to avoid a dismissal.

Click here for an audio preview of Spartak-Rubin, from Russian Football Now's podcast.

In hindsight, this may have been the match that announced Alex's presence in the Premier League. In his inaugural season with Spartak, Alex has been the glaring difference between this season's title contender and last season's disappointment which finished eighth. His distribution has ignited countryman Welliton, who has used his speed and Alex's vision to pull away from his competitors in the goal scoring race. Welliton's fifteen goals in eighteen matches are four ahead of Rubin's Alejandro Dominguez, having more than doubling the scoring recorded he'd amassing in his preceding Russian career (just over one season, 32 appearances, 10 goals).

With Dominguez and striker Alexsandr Bukharov, Rubin has their own dynamic duo. That Rubin features an Argentine attacking midfielder to counter Spartak's Brazilian engine adds another, subtle conflict to the match-up. After two seasons at Zenit and a falling-out with Dick Advocaat, Dominguez has returned to Rubin, an injection that has helped Bukharov to eight league goals and a call-up to the national team.

Rubin advocates will evoke the first meeting and point out the Bukharov did not play, the fixture falling in the middle of a seven match stretch where Bukharov was out of the lineup. In Round 12 at FK Khimki, Bukharov returned with a hat-trick and has scored goals in eight matches, including another hat-trick two weeks ago against Terek Grozny. Combined with two goals scored in Rubin's opening match, Bukharov has ten goals in 14 league matches, with eight of those goals coming in three matches. While it is normally a stretch to say one player's inclusion would make the difference in a two goal loss, Bukharov's ability to score goals in bunches makes that claim a bit more plausible when applied to Rubin.

Yet it will be Rubin's captain Sergei Semak, not Bukharov, that will be the champion's critical player. Though box-to-box is a grossly over-used term by English-language media apt to romanticize certain skill sets, Semak is what whoever the term's creator was would have imaged when box-to-box was coined. His ability to adeptly jump from a deep position into attack is the biggest reason by Rubin has scored the most goals in the league while allowing the fewest. Against the speed of Spartak's attack, he will likely spend more time in a deeper position, teaming with Kheto to try and limit the lanes through which Welliton would run, Alex would distribute.

For Spartak, the unfortunate key may be somebody who is no longer with the team. Right attacking winger Vladimir Bystrov has left Spartak to join Zenit, and although details of the move are still surfacing, Spartak will be without a key cog to their attack. It's curious why Spartak, in the middle of a title push, would agree to the sale. You could also ask why Zenit, three places below a Europa qualifying spot, is making this push now. This move could have happened in the winter. The player must have pushed the move. Zenit must find their current place unacceptable. As a result, Spartak's title hopes have taken a major hit.

Spartak's biggest asset in attack has been their speed: Welliton, Bystrov running through the defense with Alex finding them. Losing one of those two is huge. Rubin has six players either deployed into or capable of falling back into defensive roles. To have organize themselves around Welliton finding space (as opposed to two players exploiting them) makes life more difficult for Alex and Spartak's attack.

Spartak has a win from the first match and the home pitch advantage. Rubin may have a tactical edge (with Bystrov gone) and recent form, having outscored their opponents 12-1 in their last four matches.

If Rubin wins, they move a commanding four points ahead of Spartak. Spartak's lead over their place will certainly decrease from six to three points when one (or both) of CSKA and FK Moscow win. Spartak would have to split their focus between tracking down Rubin and holding off challengers for the other automatic Champions League spot. Rubin could be weeks away from being able to shift their focus to preparing for Champions League group stage.

A Spartak win would do less to disturb the league's world order, but it would allow the Rubin-Spartak dynamic that's defined this season to continue into the season's final third.

This article was originally distributed at Russian Football Now, which will be keep the good people at Mad About Fútbol up-to-date on the Russian game. The audio available in this post was part of Episode #1 of Russian Football Now's podcast.