What a difference a week makes.
Chelsea was at the bottom of Group E but two straight victories over Serie A champion AC Milan has seen it move into pole position to progress to the Champions League round of 16.
Chelsea moved to the top of the group on Tuesday with a 2-0 win at Milan, which played most of the match with 10 men after former Blues defender Fikayo Tomori was sent off in the 18th minute after also giving away a penalty.
Jorginho converted the spotkick and Pierre-Emerick Aubameyang doubled the visitors' advantage in the 34th minute to help Chelsea to its first win on Italian soil since 2003.
Chelsea moved a point above Salzburg, which drew 1-1 at Dinamo Zagreb in the other Group E match. Milan and Dinamo are three points below Chelsea.
Milan, which was going through an injury crisis, lost 3-0 at Chelsea last week. Tomori had one of Milan's worst performances and was hoping to redeem himself at San Siro.
But it all went wrong for him and Milan early on as Tomori was shown a straight red card for a tug on Mason Mount and the referee pointed to the spot.
Jorginho had missed his past three penalties for Italy but his trademark hop, skip and jump technique worked this time and he sent Milan goalkeeper Ciprian Tatarusanu the wrong way.
Milan didn't let their heads go down and almost leveled shortly after as Olivier Giroud was allowed too much space but the former Chelsea forward headed Brahim Diaz's cross wide of the right post.
Mount was again involved in Chelsea's second as the England midfielder touched on a through ball to Aubameyang, who buried it into the bottom right corner.
Sergino Dest had a great opportunity to get Milan back into the match on the hour mark, following great play by Rafael Leao, but the American blazed his effort over the bar.