Porto's Brazilian striker Hulk and Benfica's Belgian midfielder Axel Witsel both joined the side on five-year deals, with Hulk reported to have cost £39.5m and Witsel around £32.5m.
And with the Russian transfer window not closing until Thursday, more big money deals are still possible with a third huge bid expected for Manchester United and Portugal winger Nani.
Hulk was a major transfer target for Chelsea over the summer, but the Blues were unwilling - or unable - to meet Porto's valuation.
And that has left fans scratching their heads wondering how can the European and FA Cup champions playing in a money-laden league that is watched all across the world miss out to a Russian team who have never been beyond the last-16 of the Champions League.
The answer is that the side is backed by Gazprom, Russia's state-owned oil and gas company. If that sounds odd, you're not wrong: it's exactly like a pre-privatisation British Gas both owning Chelsea and bankrolling their huge expenditure in the transfer market.
Actually, that's not even close since Gazprom's £100 billion business extends well beyond mere gas as they have power in the media, construction and several other businesses. Imagine British Gas had been merged with ITV and Balfour Beatty and you might be closer.
The company - which is solely responsible for 10 per cent of the country's GDP - has close ties to Russia's President Vladimir Putin, who axed the chairman of the board when first taking power over a decade ago. Putin's series of reforms was designed to turn the company into a national 'energy champion', and its power and resources have always been behind him throughout his political career.
Gazprom's pockets are not apparently bottomless, however: they started building a new stadium for their side in 2007, which was planned to open in December 2008 with a capacity of 69,000.
The company stopped funding the stadium, however, with the local St Petersburg city government stepping in as Gazprom turned to skyscraper construction instead.
At the moment, Zenit are still playing in a temporary home, the 21,405 capacity Petrovsky Stadiium.
The move is still planned and the New Zenit Stadium, as it will be called, is now scheduled to open in 2015 with a capacity of 62,000. It will be one of the main stadiums at the 2018 World Cup, and is on course to become the most expensive arena ever built.
Whether Hulk and Witsel ever get to kick a ball in anger at that new stadium remains to be seen - but Gazprom's recent deal to sponsor the Champions League means that it's a name all football fans will be hearing a lot more from here on.