The Spaniard launched an early attack at the foot of the Category 3 climb of the Alto de Montjuic 4km from the stage finish to catch his GC rivals sleeping and extend his lead at the head of affairs.
Belgium's Philippe Gilbert (BMC) took the stage win, his first win of the season, after being the only rider to follow the Spaniard's wheel and his tactical awareness was rewarded as he sprinted past Rodriguez in the home straight to take the win. Astana's Paolo Tiralongo was the best of the rest as he left the chasing bunch in his wake to take third with Rodriguez's nearest rival, Alejandro Valverde (Movistar), coming home in sixth position.
Nicolas Roche (AG2R La Mondiale) made an effort to try and recover some of the time he lost during stage eight, but his brave effort was not to be, as despite being alive to the break, Gilbert and Rodriguez rode away from him and he was swept up by the chasers in the final metres.
Stage eight brought the riders 196.3km from Andorra la Vella into Barcelona and included two Category 3 climbs, the second one coming just a handful kilometres before an uphill drag to the finish line.
The action began early on with a quartet of riders being allowed to break away inside the first three kilometres. Following the excesses of Saturday's gruelling mountain top finish, the bunch were happy to allow Martjin Maaskant (Garmin Sharp), Javier Chacon (Andalucia), Mickael Buffaz (Cofidis) and Bertjan Lindeman (Vacansoleil) build a lead that rose to 5'20” at one point.
It was this group that contested the first climb of the day, the Category 3 ascent of the Alto de la Collada de Clara. The 6.4km climb with a 5.4% average gradient was crested first by Lindeman and he was followed over the top by Buffaz and Chacon.
At this point the escapees had a gap of 4'48” as the peloton continued to keep things under control as the riders welcomed the opportunity to take things a bit easier.
The average for the first two hours of racing was coming in at just under 40km/h, way down on Saturday's 52.6km/h for the first hour of racing.
Passing through the intermediate sprint point at Cardona, the four leaders were still some 3'48” up the road. Contesting the sprint points, Cofidis rider Buffaz made it three from three, having been involved in the break yesterday and taking both of the intermediate sprints. Lindeman took second over the line, with Chacon taking third, as he had on the previous climb.
The gap came down briefly with 80km to race, but the peloton weren't committed to the chase and on the approach to the second intermediate sprint of the day the leading quartet still held an advantage of 3'48'' over the peloton.
The peloton did eventually begin to chase with some conviction approaching the 50km to go point. The gap began to tumble and as the four leaders contested the intermediate sprint at Martorell, the bunch had closed the gap down to just 1'04”. The pressure was not enough to stop Buffaz making it four from four, winning the sprint from Lindeman and Chacon.
From here the break was doomed and with Katusha, BMC and Lotto-Belisol driving the bunch, it was only a matter of time before they were reeled in.
With 20km left to race the last of the four early leaders were reeled in and apart from a brief counter-attack by Andalucia's Jesus Rosendo, the pace was just too high for anyone else to make an escape.
The pace continued to rise into the final 15km and at one point hit 68km/h. Katusha were doing their best to control things at the front but were not having everything their own way. Rabobank, Orica Green Edge, Argos Shimano, Sky and Saxo Bank Tinkoff Bank all made their presence felt, but none of them took total control.
With 5km remaining and as the ascent of the Alto de Montjuic loomed, Alberto Contador launched a trademark stinging attack. Just as quickly as he gained a few seconds, he was reeled back in and they were all together as they hit the climb.
It was here that Rodriguez made the winning move. Astana were pushing the pace at the front of the race and as they came under the 4km to go banner, BMC's Allesandro Ballan jumped out of the front of the bunch. He was immediately chased down by Joaquin Rodriguez, Gilbert and Roche. Ballan's attack immediately failed and Roche was unable to stick the pace
With 3km left to race and as they came over the top of the climb, Rodriguez and Gilbert talked tactics and then after everything was agreed, put their heads down and pushed for home. The continued to work together and though the chasers were coming back at them rapidly, the pair held on to the line. Rodriguez was not too bothered with giving away the stage win as Gilbert wasn't really challenged when he moved around him in the final metres. The Spaniard's mind was firmly focused on the time he could gain over his rivals.
The Katusha leader will be very happy with the last two stages taking second in both. Rodriguez is now 53 seconds to the good over second place Chris Froome (Sky) and Contador at one minute as the riders head into Monday's rest day.