In the game Euwe-Smyslov (Zurich Candidates, 1953), the following position was reached after 30...Qc5-e7.
The game continued 31. Qe2 Rxd7 32. Bxd7 Qxd7 33. Qxe5+, and Black eventually won.
In David Bronstein's book on the tournament, he rejects 31. Rd1 based on the continuation 31...Rc7 32. Qe1 Nc6 33. b4 Qxb4 34. Nxe5 Qxe1+ 35. Rxe1 Nxe5 36. Rxe5 Rd2 "and Black must win." (See next diagram for this sequence.)
In the kibitzing section for this game at chessgames dot com, poster Hesam7 proposes 33. Qc3 (instead of 33. b4) 33...Rdxd7 34. Rxd7 Rxd7 35. Qxc6. (See next diagram for this sequence, starting with 31. Rd1.)
In the position reached in the above diagram, Black is up the exchange for a pawn, but converting this to a win will require finding and exploiting targets in White's position. The two obvious ones are White's b-pawn and f-pawn, each of which lies on a half-open file.
While exploiting these targets, Black mustn't overlook the main weaknesses in his own position: the isolated a- and e-pawns and his open second rank.
Let's consider where Black's pieces might ideally belong so that they could pressure White's targets while protecting Black's. Interestingly, White's f-pawn is on the same line as Black's a-pawn, and the same is true of White's b-pawn and Black's e-pawn. These facts suggest that the Black queen occupy the d4-square, from which she would control the squares occupied by all four of those pawns.
To guard Black's weak second rank, the rook would need to occupy it, but the good news is that it would have access to both b7 and f7, from which to pressure the White pawns on those files. Last but not least, Black's king would seem fairly well-sheltered at g7. (See next diagram for this setup in the absence of White's pieces.)
Now let's consider where White's pieces might belong. The b-pawn might ultimately need the bishop's protection, which suggests putting the pawn at b3 and the bishop at c4. A side benefit of having the bishop at c4 would be that it would control f7, thereby preventing Black's rook from occupying that square.
If White's queen were to also find her way to the a2/g8 diagonal (say, at d5), she might have access to g8 and then to other squares along that rank, which could harass Black's king.
It's not clear that White's king has a better spot than g1, so we'll leave it there for now. We'll imagine White's queen at e6, where she has ready access not only to g8 but to both wings. (See next diagram for this setup in the absence of Black's pieces.)
Back to the actual position...
We'll try moving the rook to b7 to threaten one of the identified targets (the b-pawn) and thereby constrain White's viable replies.
After 35...Rb7, 36. Qc8+ Kg7 37. Be6 gets White nothing after 37...Rxb2 38. Qg8+ Kh6. If instead of 37. Be6, White's queen retreats along the c-file, then White will have wasted a tempo while Black played the constructive 36...Kg7. Therefore, White's queen should retreat immediately.
We'll examine 36. Qc2 first. For the play and notes, see the diagram below.
In the ending reached above, Black's king will head for White's b-pawn, after which Black will return the exchange in order to capture both of White's queenside pawns. Then, while White's king is preoccupied by Black's passed a-pawn, Black's king will head for White's abandoned kingside pawn(s).
Now we'll examine 36. Qc1. For the play and notes, see the diagram below.
Finally, we'll analyze 36. Qc3.
This discussion seems to demonstrate that White would have been lost in the following position (where Black is to move).