diff --git a/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc b/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc
index 3ab42d89b6ee..392fd9fbb705 100644
--- a/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc
+++ b/cpp/src/arrow/compute/kernels/scalar_cast_nested.cc
@@ -346,11 +346,13 @@ struct CastStruct {
     for (int out_field_index = 0; out_field_index < out_field_count; ++out_field_index) {
       const auto& out_field = out_type.field(out_field_index);
 
-      // Take the first field with matching name, if any. Extract it from the map so it
-      // can't be reused.
-      auto maybe_in_field_index = in_fields.extract(out_field->name());
-      if (!maybe_in_field_index.empty()) {
-        fields_to_select[out_field_index] = maybe_in_field_index.mapped();
+      // Take the first field with matching name, if any. Erase it from the map so it
+      // can't be reused. Use lower_bound (which guarantees first-match) instead of
+      // find/extract (which do not guarantee first for duplicate keys).
+      auto it = in_fields.lower_bound(out_field->name());
+      if (it != in_fields.end() && it->first == out_field->name()) {
+        fields_to_select[out_field_index] = it->second;
+        in_fields.erase(it);
       } else if (out_field->nullable()) {
         fields_to_select[out_field_index] = kFillNullSentinel;
       } else {