With five stages to go – three of them summit finishes – the outcome of this year’s Vuelta a Espana remains in the balance, with podium places and top-ten finishes up for grabs. So what can we expect to happen on the pivotal mountain stages over the next three days? Here are some of the likely scenarios.

Where and when to attack?

After a flattish stage today, the riders are again faced with three consecutive summit finishes which will decide the general classification. The tactical conundrum facing the riders is to determine where and when to make their moves. No one will be able to attack flat-out on all three days.

Stage 18 has a sawtooth profile leading to the final short, sharp climb of Pena Cabarga (5.9km, 9.2% average). The leaders may well decide to hold back a little, weighing up moderate time gains against the risk of draining their reserves too soon.

Stage 19 offers the potential only for relatively small gains on a lumpy but not excessively taxing finish. 24 hours ahead of the Angliru, it looks ready-made for a breakaway.

Stage 20 is the one the riders will either fear or relish more than any other in this year’s race. It’s a short stage at 142km, which will encourage aggressive riding, with each of the four climbs getting successively tougher. There’s little respite between the summit of the cat 1 Alto del Cordal (5.3km, 9.6%) and the start of the Angliru (12.2km, 10.2%). Each climb could form the springboard for an attack, and even on the Angliru we will undoubtedly see riders attack at different points.

The steepest section of 23.5% comes relatively close to the summit – the finish is actually downhill – meaning some riders will have to attack earlier on. There’s no shortage of places to launch an offensive, not least the short downhill section after 5km.

However, while an early attack means greater potential upside, it runs the risk of a rider running out of gas just as the road turns super-steep. Get it right, and an attacker could gain two minutes or more over his rivals. Get it wrong, and they could easily lose double that amount.

Who will attack and when?

Now that we’ve looked at the parcours, let’s remind ourselves of the GC standings which will shape the various rider tactics. Here’s the top ten as of this morning:

1. Vincenzo Nibali (Astana) 64:06:01

2. Chris Horner (RadioShack-Leopard) +0:28

3. Alejandro Valverde (Movistar) +1:14

4. Joaquim Rodriguez (Katusha) +2:29

5. Domenico Pozzovivo (Ag2r La Mondiale) +3:38

6. Nicolas Roche (Saxo-Tinkoff) +3:43

7. Thibaut Pinot (FDJ) +4:37

8. Leopold Konig (NetApp-Endura) +6:17

9. Samuel Sanchez (Euskaltel-Euskadi) +7:33

10. Tanel Kangert (Astana) +9:21

For Vincenzo Nibali, the tactical outlook is uncomplicated but not easy. There is little to gain and everything to lose by attacking his closely-matched rivals. He will rely on his team – Astana still have all nine men – to manage the race, leaving him fresh to deal with the final kilometres, where his top priority will be to stick to Chris Horner’s rear wheel. He’ll want to keep an eye on Valverde and Rodriguez too, but should either Spaniard attack he will look for Horner, who must also defend his position, to make the first move.

Horner has to manage a fine balancing act. He’s just 28 seconds in arrears but also only 46 ahead of Valverde. He has no need to make any extravagant or early moves, and as long as he can hold off those immediately behind him can afford to gamble everything on one big attack in the final 2-3km of the Angliru. With time bonuses available, a 20-second gap could be enough.

The position for Valverde is trickier if he has ambitions beyond second place. To catch Nibali, he will either need one big – and therefore risky – attack on the Angliru, or perhaps look to snatch time on Pena Cabarga to make the challenge more manageable. A move on stage 19 also isn’t out of the question, although this might compromise him for the Angliru. With an advantage of just 1:15 over Rodriguez, he’s unlikely to be overly reckless and jeopardise his podium position.

On the other hand, Joaquim Rodriguez can afford to be less cautious. He has finished in the top four at grand tours five times in the past four years without winning, so the possibility of slipping back is less of a disincentive given the prospect – however remote – of reaching the top step. A 2½-minute deficit to Nibali is sizeable but not insurmountable for a rider of his explosiveness, but if he wants to roll the dice he cannot afford to wait until Saturday. If he still has the ambition and the zip in his legs, watch for him to hit Pena Cabarga hard tomorrow afternoon. Take back a minute there and it’s game on. Any less and he will have to lower his sights. Either way, he is likely to be the most aggressive of the top four.

What about everyone else? How aggressive the other top ten riders are will depend partly on physical condition but also other tactical factors such as WorldTour points and rankings.

For instance, Domenico Pozzovivo and Thibaut Pinot ride for the relatively small French teams Ag2r and FDJ, whose management may feel there is more to be gained by protecting their current positions – and the WorldTour points that go with them – than striving for a higher placing and risking disaster. Pinot can afford to be fairly aggressive. Seventh this morning, he holds buffers of 1:40 and 2:56 over Leopold Konig and Samuel Sanchez respectively. Pozzovivo, fifth, holds a slender five-second advantage over Nicolas Roche, with Pinot only 59 seconds back. One small miscalculation could easily cost him two places. Will the pair stick or twist? My bet is they’ll keep their powder dry until the Angliru.

Nicolas Roche, on the other hand, has already rolled the dice in week two and has said he will continue to attack in this final week. Pozzovivo is an eminently catchable target for what would be a maiden top-five grand tour finish. If any rider among the top GC men is going to go all-in and animate stage 18, it will be the Irishman.

We’ll understand more about NetApp’s intentions tomorrow too. Leopold Konig already has a stage under his belt and looks reasonably secure for at least a top-ten finish. Even if he does slip a place or two he and the team will have exceeded their Vuelta targets. But to move up the order he will need to find two minutes somewhere – too much to wait until the toughest sections of the Angliru. It’s possible he may try something on one of the preceding two stages to try to close the gap on Pinot – he’s far enough behind that Astana, RadioShack and Movistar will cut him a little slack – and then launch a final effort on the Angliru. Or he may sit back and defend eighth. We shall see.

We should definitely watch out for Samuel Sanchez. Euskaltel-Euskadi have both form and weight of numbers – four riders in the top 30 and a full nine-man complement. They might choose to defend their lead in the team competition, but I’m sure they would happily trade that for a stage victory. If so, the move will come on stage 19 in Oviedo, which just happens to be the home town of both Sanchez and incoming team owner Fernando Alonso. Watch for the orange jerseys to have a quiet day tomorrow and then seize the initiative on Friday.

Of course, attacks aren’t limited to those within the top ten. Teams who have failed to taste success so far (ahem, Lampre-Merida) and riders who have slipped down the order will go on the attack in the hope that the contenders are preoccupied with marking each other. Watch out for Amets Txurruka (Caja Rural), who has been prominent throughout, Michele Scarponi (Lampre), the Sky pair of Rigoberto Uran and Sergio Henao, Jerome Coppel (Cofidis) and perhaps the redoubtable Adam Hansen (Lotto-Belisol), who stands just five days away from the remarkable achievement of completing each of the last seven grand tours dating back to the 2011 Vuelta.

One final tactical curve-ball: we might see Katusha or Movistar looking to insert one or more men into a break, offering the option of a longer-range relay for Rodriguez or Valverde. Sound familiar? It’s the same tactic used by Saxo last year which propelled Alberto Contador to a stage win and ultimately overall victory. In an ideal world, Astana would shut this down before it becomes too big a threat, but it’s a tough tactical call to make, especially if attacks are coming from other directions too.

What will happen? Who knows. Many tactical options are still possible, and we can be sure every team will have spent the rest day devising various scenarios. The cards have been shuffled. Let’s see how this final hand plays out.