Remarkably that represents an all-time high for the double world champion, with the Rankings being introduced after the last of his drivers' crowns in 2006.
The race was won in typically dominant fashion by Sebastian Vettel, who now has a seemingly unshakeable lead in both the 2011 championship and the Rankings.
Webber had been second in both disciplines heading into Monza, but crashed early on after clashing with Felipe Massa - an incident he later conceded made the rest of the season a 'battle for second'.
The retirement left Webber's position in the Rankings vulnerable, presenting Alonso with an opportunity he duly seized when he finished on the podium, having withstood heavy late pressure from the charging McLaren of Lewis Hamilton.
Alonso's move into second overall not only represents his highest ever position, but is only the second occasion in the past 12 months that Webber has been demoted from second in the standings.
Jenson Button also closed in on Webber, rising two places to sixth overall, while Lewis Hamilton stayed fifth but lost ground after dropping his victory at Spa last year under the rollover system.
Button's progress means seven-time WRC champion Sebastien Loeb is the only non-F1 man inside the top six.
Across in the UK the AUTOSPORT 6 Hours of Silverstone caused some dramatic moves in the Rankings, with the race-winning Peugeot duo of Sebastien Bourdais and Simon Pagenaud rising by a combined total of 65 places. Bourdais now sits 35th, with Pagenaud slightly lower in 66th. They were harried throughout the race by Audi, whose four drivers also made significant gains - Allan McNish improving the most as he leapt 64 places to 146th.
To see the full Castrol Rankings and the latest positions in the Race for 2011, please visit www.castroldriverrankings.com.